A friend(no 'benefits') who's so close she's like a sister, or just is the mother of someone who calls you Uncle. (could be a former sexual partner, but who is only a friend now)
How many siblings do you have?

Well, I have 2 brothers, 2 sisters from my mom, & a half brother from my dad, & a courtesy sister I stilll keep in touch with.
by cyberpope67,BC,Canada May 2, 2021
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