I’m going to proceed on the assumption that the unicorn in question, though a sentient creature, is basically a horse in anatomy. I prefer to have the story grounded in reality in some small way.
I think the closest analog to how a horse feels is a really big Dobermann or pit bull. They have the same short, close, smooth, wiry hair and the same tightness of skin over hard muscle that horses have. Horses feel like one ton pit bulls, there you go! Sitting up on a horse’s back feels like a mile off the ground and on a wide barrelled horse it’s possible to turn around, put your feet up on its butt and lean back along the neck like a big old chaise longue. The nose is like velvet, the ears are like plush. If you stand next to a horse’s head and tuck your shoulder underneath its neck you can wrap your arm all the way around its head and maybe get your hand across the nose–that’s how big the head is. If you want a horse to move over you can bump 'em on the shoulder or on the rump and they’ll usually shift over. If you bump the back of their knee they’ll pick their feet up for handling–if they trust you. A horse with one foot up is a vulnerable horse and they know it. Horses have a spot on their necks, up under the mane maybe three hands widths above the withers (shoulder) that when scritched makes them go limp and zonky–it’s like a dog’s scritchy spot. That’s the spot that another horse will nibble on to make friends.
The really amazing thing is that they are so huge they could kill you without even trying (I’ve seen a horse bite a grown man on the shoulder and pick him right up off the ground) but they don’t–they tend to be fairly timid and want to get along with everybody.
Oh, and male horses will sometimes relax their belly muscles and drag their dicks on the ground. To make them pull it back up you pretty much have to boot them right in the flank (the area where the back leg and belly meet) and they’ll haul it in. Don’t kick a horse in the flank while you’re sitting on it, though, unless you wanna learn how to fly! It’s sensitive, y’see…
Not mentioninng dicks in this story. Not even a tiny bit.
Not even with the whole unicorn and virgins thing?
Even geldings will let their penis droop out of the sheath when taking a pee. Used to alternately fascinate and horrify us little girls during horseback riding lessons. Newbie: “What’s he…doing??”
Rest of us, exchanging glances: “Um…well, he’s going to pee!”
Newbie: “Nooo!”
Us: “Yes! Fer sure!”
[shocked giggles all around]
You’ll just have to have your unicorn “hold it” for the duration of the scene. 
There, got that for ya. 
Regarding the OP, I have little to add to the previous replies, other than the word “supple”. To me this is the adjective for describing a horse’s coat. Maybe it’s too trite or hackneyed for your purposes but sometimes there’s a reason a word or saying becomes cliched.
In light of your subject being a unicorn, you might add some modifier such as charged (suppleness) to imply the preternatural.
I don’t read [del]much[/del] any fantasy, so all apologies if I’ve just plagiarized “Describing Unicorns for Dummies.”
OtakuLoki’s description pretty much nailed it for me. Horses are very much prey animals, and even at the quietest moments they are intensely aware of their surroundings. “Still waters run deep” doesn’t even begin to describe how it feels to walk through a herd.
They’re also social, and there is a literal “pecking order” in every herd. In the few herds that I have been around, every horse except one or maybe two had at least a few bite marks on their hide–small scabs, usually about the size of a closed staple. This pecking order shouldn’t include humans, though that may depend on how they are treated and trained.
Where do you live? Maybe someone could recommend a farm with a lot of horses in turnout. It would be a shame if you based your ideas of what a horse is like on horses kept in stalls with little chance to interact with one another.
I have nothing new to add to the thread. I just wanted to let y’all know that, as I mentioned in the OP, and as several of you advised, I not only went to touch a horse this weekend, but actually rode one. riding this weekend. I won’t try to describe how great it was (though my ass aches! why was I not warned about that ! You will all pay! ) because I am frankly too busy–but those of you who told me how wonderful horses are were completely right.
blinks But we thought you’d have done some basic research.
Haven’t you heard of that old cavalry manual that is still being bandied about as the ultimate description of riding and campaigning from horseback:
Forty Miles in the Saddle, by MAJ Assburns.
You’ll pay for this. You, and your children, and your children’s children’s children (but not your children’s children, for complicated vengance-swearing reasons.)
Did you touch the horsie’s nose?
Yes. That was really the point of the exercise, because of the descriptions given upthread it was teh most vivid, and most surprising (to me), and I’d have been content to stop with doing that and stroking its main and neck. But Mrs. Rhymer wanted to ride, and she didn’t want to do it alone.
Amen. And after having an apple or two, their breath smells even more lovely.
If I could bottle how you feel when you have loved and been loved back by a horse into a pill, no one would ever need drugs again.
The animals most people are familiar with are dogs and cats. Maybe sheep and goats at a petting zoo. In comparison to these animals, a horse’s hair is more bristly or slick - you won’t be able to run your fingers through a horse’s hair. Another noticable difference is that a horse’s skin seems to be stretched tautly over its body - you can feel the bones and muscles right below the skin with no looseness or apparent layer of fat.
What’s really lovely is when you stand by the horses head, facing its back, and you slip the arm nearest the horse under the neck to pat the other side of the neck, whilst patting this side of the neck with your other arm. Then your horse relaxes and drops his head so that his cheek is resting on your shoulder. Awesome.
My darling Ben (grey Anglo-Arab, fifteen hands of personality) also used to rest his chin on my head when I sat down on the grass in front of him. And fall asleep. Awesome.
He also used to fall asleep when my dad was filing his hooves, and would start leaning pretty heavily on dad. Not so awesome when he got a file slapped on his rump to wake him up. The horse, that is, not my dad.
Can it really be that hard to go find a horse to pet? Heck, I live in Chicago and there are plenty around for carriage rides and occasional mounted police officer. A quick trip to the suburbs will find a smattering of stables where you can rent horses (and probably pet them for free). A trip to the zoo and the petting area for kids will likely have ponies there to be pet (which still feel like petting a horse just without all the imposing size…better to experience the full-blown horse but pony = less intimidating).
And not all horses are docile creatures. Generally the younger they are the more…high strung (for lack of a better word) they are. I would only deal with those with a handler who had experience with that horse or if I was an expert rider. The older a horse gets they tend to mellow out a lot (they can get pretty old…into their 30’s). Usually past 12 years they seem fairly mellow and approachable by most people. Of course most places where you could encounter a horse up close the horses will be fine and used to such approaches. Still ask the owner first just to be sure.
I’m guessing you didn’t actually read, oh, any part of the thread other than the title. In the future you may wish to do so to avoid looking silly.
I’m way too phobic to pet a dog, sorry.
I had my very first horse-petting experience two weeks ago. It was brief, at a “Living Museum” kind of place. I remember two things:
- The head was ENORMOUS.
- The mane was greasy at the roots and very dry at the ends.
He was a sweet horse, it’s just that those are the two things that surprised me.
I came in here to say pretty much this. Rippling, working muscles under the skin - it’s an experience consisting of contrast.
Also, I always kind of get the impression that here is an animal that could - if it wished - easily destroy me but - graciously - probably won’t.