The gaffer gives a chap warning (7)
I believe the answer is:
foreman
'the gaffer' is the definition.
(synonyms)
'a chap warning' is the wordplay.
I cannot quite see how this works, but
'a' could be 'an' and 'an' is found within the answer.
'chap' could be 'rem' and 'rem' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
'gives' acts as a link.
Can you help me to learn more?
(Other definitions for foreman that I've seen before include "Supervising worker" , "spokesman" , "Charge hand" , "Gaffer, boss" , "Fellow in charge" .)