to believe that sth is true, especially sth that is not very likely
You could say you were ill but I don't think they'd buy it(accept the explanation).
by irearn May 22, 2007
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To take part in the system. Or become mainstream.
"I didn't sell out, Son, I bought in. Keep that in mind."
- Dad, SLC punk

The punk band did a total sell-out buy-in.
by Jamaal Ahmed June 28, 2004
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Something you do when you can't find it on a peer-to-peer app.
I've even tried SoulSeek to get the Barry Manalow LP, shit I'll have to buy
by joly1 September 26, 2003
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a really, really hot asian guy
That bui has got a nice booty.
by nghiem June 23, 2004
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A word of greeting amongst typically, but not exclusively, male Chavs, Townies and Scally's. Derived from the mispronunciation of the word 'boy', it is often used multiple times in the same sentence. It is most commonly used in a friendly manner, although when the enevitable eruption of tension and/or violence occurs between members of the community(ies) to which it belongs, it will be replaced, ironically, with the word 'mate'.
Male 1: "Alright buy? What's 'appnin buy?"

Male 2: "'ere buy did you see the buy other day what smashed that window down KFC in town?"

Male 1: "fuckin' 'ell buy yeh what a nutter innit buy!"

Male 2: "Yeh I know buy. Fuckin' gonna smash the cunt's 'ead in buy my fuckin' sister was fuckin' workin in there at the time wunnit buy. And she's fuckin' pregnant!"

(cycle down to next estate on BMX bikes)

Male 2 to Male 3: "Oi mate! You fuckin' smashed that window down KFC mate my fuckin' sister was workin in there and you nearly killed 'er fuckin baby. You're fuckin dead mate!"
by sd999 February 11, 2014
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When something's REALLY important. The tags "bold," "underline," and "italicize" begin with the letters BUI, hence the term. When someone using BBCode BUIs something, you know shit's about to go down.
Oh damn, he BUI'd "but." There had better be a good reason.
by MegamanTTEX November 2, 2010
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