It occurred to me that I’ve heard it said and written both ways. Which is proper?
I always hear it as “Butcher’s Knife.” But it might be subject to local variations, like “Coke,” “Soda,” “Soft Drink,” “Cola,” etc. Higher in the east and south.
Is one a type of knife while the other is a person’s property?
I don’t know, but I always say Butcher Knife. I’ve heard it the other way, not that often, it doesn’t sound wrong either way.
The main websites selling knives that pop up on google seem to all say butcher knife. At least on the first couple of pages that I could bother myself to look at. That’s how I always say it. And it’s a butcher block too.
When someone has come at me with one, I’ve never stayed long enough to find out. 
What if he came at you with a banana?
How about a pointed stick?
I’d thank him a bunch.
You sure do have cheap taste in kitchen cutlery.
I have only heard “butcher knife” in Arkansas and Tennessee.
I once stabbed a man in Tennessee with a Butcher’s Knife, just to hear him correct my use of apostrophes.
Very good
Yeah? Well, I once stabbed a man in Tennessee with a Butcher’s Knife, just to THANK him for correcting my use of apostrophes.
Funny thing; he had a hole in his shirt for the knife to go in, almost like he was EXPECTING someone to stab him. Maybe it’s a Bible Belt thing; they’re always talking about the “stabitude of gratitude,” or some such nonsense.
Butcher’s knife.
Butchers use boning knives, breaking knives, skinning knives, paring knives, carving knives, cleavers, etc… One knife could do it all but different designs makes butchering easier and more efficient.
A “Butcher’s Knife” is a heavy bladed knife used primarily for butchering meat into separate sections (such as cutting a hind quarter into smaller sections) which are then separated by muscle texture and cookability. Roast meats and steak meats aren’t usually cooked together or by the same method (except for slow roasting an entire hind quarter).
The thick, heavy blade of a butcher’s knife adds heft to provide optimal leverage for separating meat from bone.
Butcher’s knife -
According to noted pedant and linguistician Jayne Cobb, it’s “butcher’s knife”:
Zoë: Where’s River at now?
Mal: In her room, which I’m thinking we bolt from the outside from now on.
Wash: That’s a little extreme, isn’t it?
Jayne: Anybody remember her coming at me with a butcher’s knife?
Wash: Wacky fun.
Jayne: You wanna go, little man?
Wash: Only if it’s someplace with candlelight.
Zoë: Sir, I know she’s unpredictable, but I don’t think she’d harm anyone.
Jayne: Butcher’s knife!
Zoë: Anyone we can’t spare.
A butcher’s knife could be any knife owned by a butcher. So it’s ambiguous if you use the possesive form.
I say butcher’s knife, by analogy with the chef’s knife - no-one ever says “chef knife”
Butchers’ knife.
It is a knife type that is used by a lot of butchers, not just one.
Don’t you all have fingers to type google.com? It is butcher knife. A butcher knife is a knife used to butcher.