A bighead, for instance, can be a mendicant (3)
I believe the answer is:
beg
'be a mendicant' is the definition.
(I've seen this in another clue)
'a bighead for instance' is the wordplay.
'a bighead' becomes 'b' (the head letter of 'big').
'for instance' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'b'+'eg'='BEG'
'can' acts as a link.
(Other definitions for beg that I've seen before include "Beseech or ask for charity" , "Plead or scrounge" , "Plead in desperation" , "Solicit charity" , "Plead or importune" .)