Given food by a fatheaded fellow (3)
I believe the answer is:
fed
'given food' is the definition.
(I've seen this in another clue)
'by a fatheaded fellow' is the wordplay.
'by' means one lot of letters go next to another.
'a fatheaded' becomes 'f' (this could be a standard abbreviation which I don't know about).
'fellow' becomes 'ed' (short for Edward).
'f' put next to 'ed' is 'FED'.
Can you help me to learn more?
(Other definitions for fed that I've seen before include "Nourished" , "Banking authority" , "US agent" , "Gave food to (someone)" , "Provided food for" .)