The crossword solution for the term LIP-___ (PRETEND TO SING) is 'SYNC' (4 letters). Lip-sync is a form of performance art in which a person pretends to sing or speak by moving their lips in synchronization with a recorded vocal track. It is commonly used in music videos, television shows, and live performances. Lip-sync is also used in film and theatre, where it is often referred to as 'mouthing'.