scissors - they’re plural, and are referred to as a pair of scissors.
so what is a scissor, other than being a sharp knife? was the item (or the word) ever used in the singular, until someone joined two blades together?
According to Wiktionary, scissors (plural) seems to have been the norm from Vulgar Latin through Middle French through Middle English. (I’m rusty on Latin plurals, so if anyone can correct me on that, please do so.)
Merriam-Webster says that scissor (singular) dates from the 15th century, while scissors (plural) is about a century older.
My educated guess? No such thing as a scissor until we had a pair of scissors and needed a name for when it was broke in half. 
OED does have examples of a singular form, although it is now obsolete.
Chisel, by the way, is a cognate, ie both words descend from the same (French) root word.
A scissor is, obviously, what one uses when making clothing to cut out one pant.
So, like lessor and lessee, you’ve got your scissors and your scissees.
The scissees being “that which is scissed.”
Either that, or the whole thing has something to do with tits? 
Hmmmm… cleavage…
Sorry, where were we? Oh, yes, shears. … Hmmm cleavage…
Sorry, carry on.
Yeah, chisel is probably the root.
Scissors is cited the earliest in English in Chaucer’s House of Fame, 1380 as
.
It was borrowed from Old French cisoiries, which occurred just before Chaucer’s time, which was borrowed from Vulgar Latin cisoria, which wasn’t really vulgar but was the language the people spoke in the 6-10th century or so, having ditched the more formal Latin of the earlier period closer to the 1-4 centuries. These were all borrowed from the original Latin compounds such as excisus, which was a past participle of excidere, meaning to cut out.
It might (or might not) be worth pointing out that in French, ciseau is a chisel, while ciseaux are scissors (or more than one chisel).
Could the root be incise?
If you take a pair of scissors apart, I would think that each part would be a scissor.
A scissor is something which scisses. You sciss with a scissor.
I’m getting a headache.
I have never scissed, not have I scissorsed, but I have scissored.
You scissor? Well, I rock.
hey and also, scissor is used in the context of “cutting”. In my line of work, we use it in a totally different context, where a direction might be, “get them to scissor” (aka, trib).
Of course, scissoring is now used to describe the motion of other mechanical contraptions, such as levers connected by an axis, which is what scissors really are. A scissor lift, for example.
How much cleavage would one need to scissor?