Very small measurement used by toolmakers & engineers, or roughly .0001 or one ten thousandth of an inch. Actual size may vary between shops, but always much less than a pussy hair. About one tenth of a skosh which is equal to approximately one nudge of the dial.

Note: When specified, generally regarded as smaller than the smallest one can measure or produce, since while most people intuitively understand that a gnat's ass is pretty small, few have actually bothered a gnat to measure one.
"Clearance is clearance, Clarance, but that die is only missing by a gnat's ass".
by aethernet September 3, 2006
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Guy 1: Did you see the newbie at the party? I couldn't get near her all night.

Guy 2: Oh, yeah I saw her. I worked the floor for two hours and I was a gnat's ass away from her when she left with her friend.
by italknerdy October 28, 2011
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Jon measured the wall and told me it was gnats ass!
by Genofam October 9, 2008
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Some one who unbeknownst to them is hated by all due to their stupidity, constant ability to be conveniently where you are at any given time, overly available, lacking a personality, a douche, a duck, stage 5 clincher, desperation friends even shun this person. They are like an irritating shadow that just never knows when to go the Fuck home, or die off....even when invited blatantly to do so. This person sucks and is the ass of everyone's joke, the third unwanted wheel and destined to masturbate alone to the sci-fi channel with a pint of cherry Garcia ice cream in their parents house until they are over 40 years old. No one cares, notices or cries when this person dies, disappears or moves away....they celebrate, clap, and smile all day long when this happens. People try to set this person on fire or back over them with vehicles. People's moms are the only friend of an ass gnat. I don't know why but moms love that shit.
Caleb is such a fucking ass gnat, I couldn't get rid if him if I tried.
by Ihateyourfacedaily85 January 23, 2015
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a name given to someone who never ceases to annoy me
YOU: Hey dude!
YOU: Hey man!
YOU: Dude!
YOU: Dude, hey!
YOU: Dude look!
ME: WHAT, ASS GNAT????!!!!! WHAT THE HELL DO YOU WANT?????!!!!!
by BOSS HOSS January 8, 2008
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