The terms and their definitions used in firearms have evolved with the evolution of the arms themselves. As far as I know, there is no "Blackstone's legal dictionary" of gun terms.
There are many glossaries, none of which is, or could be all inclusive.
The terms come from many sources, over a lot of time, and there is an inextricable mixture of use in both technical discussions and regular conversation.
There are terms defined by the military.
There are terms defined by individual gun makers.
There are terms accepted as "industry standard"
There are terms defined by their general use in the shooting community.
There are terms defined by their use and misuse in casual conversation.
There are terms defined by the common use, despite having a different definition in technical use.
There are even terms defined by anti-gunners.
Ordinary dictionaries are of little use, despite being the traditional standard reference for most things. And they even say so, if you read the right part.
Dictionaries state that their definitions are what is found in common usage.
When discussing any technical field, common use of a word may or may not be relevant.
And, to further muddy the issue, a technical misuse of a term can become the "commonly used" definition.
Various examples include...
Motor vs. Engine (automotive)
Clip vs. Magazine
Revolver vs. Pistol
Assault Weapon
there are many others.
Asking about a term you've never heard, or heard used that way is fine. Assuming it's not a valid term because you couldn't find supporting evidence immediately, and arguing about it,...not so much.