A person who is subservient in the relationship based purely on sexual intercourse. They will do anything if it means getting more sex.

Similar to: Under the thumb.
Tony: "Where is Alex?"

Matt: "He's not out tonight. He's totally under the tongue by his new girlfriend"

Tony: "Too busy having sex to come hang with the guys!"
by Gregtron January 22, 2011
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The fatty tongue under your real tongue. If you have a "fatty mouth" you most likely have an Under Tongue.
Mouths with under tongue are usually better when giving oral.
My girl has an Under Tongue so you know that head is on point.
by StefVonE December 2, 2022
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