lip-synch vs lip-sync

lip-synch and lip-sync both are verbs.

Word	Noun	Adjective	Verb	Adverb
lip-synch	No	No	Yes	No
lip-sync	No	No	Yes	No

As verbs, lip-synch and lip-sync are synonyms defined as:

lip-synch and lip-sync: move the lips in synchronization (with recorded speech or song)

lip-synch (verb)	lip-sync (verb)
move the lips in synchronization (with recorded speech or song)	move the lips in synchronization (with recorded speech or song)