When two brothers double up on a skank.
Jenny was getting banged by some dude when his brother walked in, and she was like, "Join us, Buckwheat, for a bronage a trois!". And he did.
by Flimsygirl July 13, 2016
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When two bros decide to add a third bro to their brolatioship. The third bro can move in with the two existing bros in their living space or he can adopt both bros into his own. While the three males may all be completely heterosexual (see totally straight), by this point at least one bro is usually able to willingly identify himself as being bromosexual.

It derives from the french "menage a trios" (meaning household of three) and the english "bro".
Bro 1: You seem like a pretty chill bro. Want to start a brolationship?

Bro 2: I already have one.

Bro 1: Bronage a trois then?

Bro 2: Hellz yeah!
by ILoveYouBro November 24, 2010
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A play on the word ménage a Trois.

When a girl is fucking with two dudes at the same time, but the guys are cool with it because they agreed to it beforehand without her knowledge.
Tiffany: You know Keisha’s been fucking with David behind your back for months now!

Reggie: Yeah, we both know how she gets down, so we have a Bronage a Trois going on.
by Mr.YumYum January 5, 2021
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