Employ wonky rebec at the start for lullaby (8)
I believe the answer is:
berceuse
'lullaby' is the definition.
(I've seen this before)
'employ wonky rebec at the start' is the wordplay.
'employ' becomes 'use' (synonyms).
'wonky' is an anagram indicator (I've seen this in other clues).
'at the start' means one lot of letters go next to another.
'rebec' with letters rearranged gives 'berce'.
'use' after 'berce' is 'BERCEUSE'.
'for' is the link.
(Other definitions for berceuse that I've seen before include "Cradle-song" , "Lullaby" .)