"Nice one. ...That was another Prince hex, wasn't it?"
-- Ron Weasley after Harry hexed Peeves (HBP19)
A jinx that glues the target’s tongue to the roof of his or her mouth.
Source: The Half-Blood Prince
References from the canon
Jinxes and hexes
"lang" Eng. language (which derives from L. lingua tongue, language) + "lock" Eng. to fasten