A woman who is obviously a lesbian but tries to hide it.
(Ain't a lesbian...ergo, lesbiaint.) Lesbiaints have been known to marry men to hide their gayness from friends, co-workers and, most importantly, their family.)
"Hey did you ever notice how Christine looks at that hot girl in personnel?"
"Of course, dude, Christine is a total dyke but she tries to hide it. Look at her hair, her clothes. Total rug-muncher."
"No way man, she was married!"
"That was a 'cover-marriage' dude. She's definitely a lesbiaint."