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1 definition by xmasfox

A person, usually a woman, who avoids risque sexual activities, especially those involving a "backside" nature. The phrase derives from the tendency of functional groups attached to t-butyl to avoid participating in chemical reactions due to steric hindrance. Often affectionately abbreviated as t-but (pronounced t-buit).
Guy: Man that nun is hot!
Other Guy: Yea but I'm sure that she's a t-butyl!
by xmasfox March 23, 2008