The friend of an attractive female that must be slept with in order to get into the pants of the female that you're really attracted to.

From ante- meaning "before" and the informal "girl" meaning "a grown woman."
Person A: How long have you been with her?
Person B: Not that long, she's only my antegirl. But wait until you see the girl that I'll have after her. She's ill
by Christopher Walch March 25, 2005
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