Second record is hard work (4)
I believe the answer is:
slog
'is hard work' is the definition.
(I've seen this before)
'second record' is the wordplay.
'second' becomes 's' (common abbreviation).
'record' becomes 'log' (log is a kind of record).
's'+'log'='SLOG'
(Other definitions for slog that I've seen before include "Work doggedly" , "big hit" , "Very tiring work" , "almighty wallop" , "Long tedious task" .)