My dictionary, which is now getting to be old at 2002 as its date, adds an interesting wrinkle into my thoughts on the subject of scissor/scissors.
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scissor seems to be described as a cutting instrument. (with no description).
Scissors is a cutting instrument with two blades whose cutting edges slide past each other.
So they both are cutting instruments, but one specifically has two blades.
Now the verb scissor is described as, to cut, cut up, or cut off with scissors or shears.
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My words::not the dictionary::
So if you need to scissor then you will need scissors; scissor or a scissor just won't do the job.
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Then I thought::
to cut, cut up, or cut off with scissors.
not a pair of scissors
not a scissors
just scissors.
But does the dictionary have to use good grammar.