Cold spell beginning to settle down (4)
I believe the answer is:
snap
'cold spell' is the definition.
(I've seen this before)
'beginning to settle down' is the wordplay.
'beginning to' says to take the initial letters.
'down' becomes 'nap' (close in meaning in sense of hairy surface).
The first letter of 'settle' is 's'.
's'+'nap'='SNAP'
(Other definitions for snap that I've seen before include "unexpected? > Same here!" , "give way" , "Break sharply like dried twig" , "you may take on holiday" , "Break under strain" .)