base of the tongue; root of the tongue
Primarily used in the set phrase 舌の根の乾かぬうち (before the root of the tongue dries; i.e., no sooner than one has said something). Rarely used outside this idiom.
See also: 舌の根の乾かぬうち
The phrase 舌の根の乾かぬうちに refers to contradicting oneself right after saying something.
Compound of 舌 (tongue) + の (possessive particle) + 根 (root). The literal meaning is 'root of the tongue'.