lip-synch
verb
ˈlip-ˌsiŋk 
variants or lip-sync
lip-synched or lip-synced; lip-synching or lip-syncing; lip-synchs or lip-syncs
transitive verb
: to pretend to sing or say at precisely the same time with recorded sound
She lip-synched the song that was playing on the radio.
intransitive verb
: to lip-synch something
It was obvious that she was lip-synching.
lip sync noun
lip-syncher noun
or lip-syncer
Word History
First Known Use
circa 1961, in the meaning defined at transitive sense