Fool sad in cold north (5)
I believe the answer is:
clown
'fool' is the definition.
(clown is a kind of fool)
'sad in cold north' is the wordplay.
'sad' becomes 'low' (I've seen this in other clues).
'in' indicates putting letters inside.
'cold' becomes 'c' (eg on taps).
'north' becomes 'N' (synonyms).
'c'+'n'='cn'
'low' going inside 'cn' is 'CLOWN'.
(Other definitions for clown that I've seen before include "Red-nosed, long-shoed entertainer" , "Funny man in circus" , "Circus comedian" , "Jester" , "Long-booted, bow tie-twirling circus entertainer" .)