A bit of a stare from Jack (3)
I believe the answer is:
tar
'jack' is the definition.
(both are informal terms for sailor)
'a bit of a stare from' is the wordplay.
'a bit of' says the answer is hidden in the clue.
'TAR' is hidden within 'stare from'.
(Other definitions for tar that I've seen before include "Thick, sticky liquid distilled from coal" , "Tobacco residue; sailor" , "Informal sailor or road surfacing material" , "Viscous bituminous substance" , "Mariner, old salt" .)