Large dull fellow to stand around idly (4)
I believe the answer is:
loaf
'stand around idly' is the definition.
(to loaf is to be lazy)
'large dull fellow' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'dull fellow' becomes 'oaf' (an oaf is a dull or stupid person).
'l'+'oaf'='LOAF'
'to' acts as a link.
(Other definitions for loaf that I've seen before include "bloomer, perhaps" , "Bread - use yours to think?" , "Head - bread" , "Some bread; 10 (slang)" , "To take things easy" .)