For fathead to have a meal is quite an achievement! (4)
I believe the answer is:
feat
'quite an achievement' is the definition.
(I've seen this in another clue)
'for fathead to have a meal' is the wordplay.
I cannot really see how this works, but
'fathead' could be 'f' (head letter of 'fat') and 'f' is located in the answer.
'have' could be 'eat' (eating is a kind of having) and 'eat' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'is' acts as a link.
Can you help me to learn more?
(Other definitions for feat that I've seen before include "Notable act" , "Great deed" , "An accomplishment of fate" , "Courageous act" , "Significant achievement" .)