when you're jacking off and you're not really feeling it yet but you cum anyways and you end up feeling horny again soon thereafter. usually happens when you're in a rush or about to get caught.
i was wacking it to some hot pics of jenna juggs 'til i heard someone knocking and i half-gasmed. total buzzkill.
by silly hats only September 02, 2008

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Top Definition
When masturbating, holding back for too long and then letting go, only to find that you've missed the orgasm, but still ejaculated. Disappointing, all the work but none of the reward.
I jerked for 30 minutes only to be rewarded with a half-gasm.
by ()*%^$#@&! March 21, 2006

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The act of having an orgasm that doesn't give you pleasure. A small amount of cum is released, but the intial feeling of an orgasm is not there. Is normally the result of some bad internal timing.
Joe: How'd it go with Susie last night?
Bob: Terrible, I only had a halfgasm.
by King Singh December 08, 2008

The Urban Dictionary Mug

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The Urban Dictionary Mug

Lotsa space for your liquids.

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The Urban Dictionary Mug

Your favorite word on a white mug.

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The Urban Dictionary Mug

One side has the word, one side has the definition. Microwave and dishwasher safe. Lotsa space for your liquids.

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The Urban Dictionary T-Shirt

Soft and offensive. Just like you.

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The Urban Dictionary T-Shirt

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A physical and emotional sensation experienced at the peak of an exciting situation that is roughly half as sensational as the sexual sensation resulting from the stimulation of the sexual organ.
This sandwich is so good it is giving me a halfgasm!
by ianbrunner November 16, 2008

The Urban Dictionary Mug

Lotsa space for your liquids.

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The Urban Dictionary Mug

Lotsa space for your liquids.

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The Urban Dictionary Mug

Your favorite word on a white mug.

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The Urban Dictionary Mug

One side has the word, one side has the definition. Microwave and dishwasher safe. Lotsa space for your liquids.

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The Urban Dictionary T-Shirt

Soft and offensive. Just like you.

Buy the t-shirt

The Urban Dictionary T-Shirt

Smooth, soft, slim fit American Apparel shirt. Custom printed. 100% fine jersey cotton, except for heather grey (90% cotton).

Buy the t-shirt