Second sleep break (4)
I believe the answer is:
snap
'break' is the definition.
(snapping is a kind of breaking)
'second sleep' is the wordplay.
'second' becomes 's' (common abbreviation).
'sleep' becomes 'nap' (I've seen this before**).
's'+'nap'='SNAP'
(Other definitions for snap that I've seen before include "Photograph - without warning" , "Bite at or utter angry words" , "Break; bite suddenly" , "Break with a crack" , "Lose cool" .)