The gaffer gives a chap warning (7)
I believe the answer is:
foreman
'the gaffer' is the definition.
('foreman' can be a synonym of 'gaffer')
'a chap warning' is the wordplay.
I cannot quite see how this works, but
'a' could be 'an' and 'an' is located in the answer.
'chap' could be 'rem' and 'rem' is located 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" .)