A 'fourthy' is a partial erection. One might be apt to call it a half-boner, but this would be technically incorrect as a 'fourthy' occurs when a penis is more than 1/4th of the way up...hence, a fourthy.

It should be noted that fourthies (plural form) are apt to occur at inopportune times (such as in public places) and as such are typically surpressed to prevent a complete erection.

If a complete erection does take place, it would be said that 'he has a boner', not a 'fourthy'.

In most cases fourthies are largely unsightly however exceptions are known to occur.
OMG that milf gave me such a fourthy.

Joey's such a pussy, when she kissed him on the cheek he got a fourthy.
by tmkly3 October 15, 2007
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A insult used to describe a member of a 3 person squad (typically Battle Royale type games) that is so bad they are hurting their squad and helping the enemies win. Almost as if they were a fourth member of a enemy squad.
Just had a match with a fourthy that threw the game giving away our position.
by Indirectllama March 25, 2021
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1/4 of an already smoked cigarette, preferred by mostly bum's or douche bags who don't buy their own cigarettes.
{See~Halfie}
"Hey can I get a cigarette from you?"
"No. But you can have that Fourthie I left in the ash tray"
".......Awww.......Fine, (grabs fourthie)"
"You Fuckin Fiend!"
by Dizzie D May 28, 2008
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