Look as jolly as Roger (4)
I believe the answer is:
grin
'look' is the definition.
(I know that grin is a type of look)
'as jolly as roger' is the wordplay.
I cannot quite see how this works, but
'as' could be 'in' (I've seen this in other clues) and 'in' is present in the answer.
'roger' could be 'r' (abbreviation used in radio communications) and 'r' is present in the answer.
A single letter 'g' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for grin that I've seen before include "Smile while pulling back the lips" , "Smile wryly" , "Happy expression" , "Give a broad smile" , "Facial expression, usually of pleasure" .)