What a fisherman may do to get in touch with a friend? (4,1,4)
I believe the answer is:
drop a line
'what a fisherman may do to get in touch' is the definition.
The definition suggests a singular noun but the answer is not.
'with a friend?' is the wordplay.
'with' indicates putting letters inside.
'friend?' becomes 'dropline' (I can't explain this - if you can you should believe this answer much more).
'a' inserted within 'dropline' is 'DROP A LINE'.
Can you help me to learn more?
(Another definition for drop a line that I've seen is " Write".)