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An involuntary burst of magic from a unicorn's horn.
Twilight Sparkle had a huge horngasm when Rainbow Dash first did the Sonic Rainboom.
by DK_The_White November 12, 2011
A slang word developed and used by highschool marching band students to convey a sense of admiration, often bordering on sexual arousal. Induced either by an especially complex and well-executed piece of music or an exceptionally well-crafted musical instrument.
Bandmember A: Did you here the Blue Cavaliers' trumpet solo in the DCI championships?

Bandmember B: Oh man...horngasm

Bandmember A: *nods* Horngasm
by Mob Barley December 28, 2004