Some pay earned for a period (4)
I believe the answer is:
year
'a period' is the definition.
(year is a kind of period)
'some pay earned for' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'YEAR' is hidden in the letters of 'pay earned for'.
(Other definitions for year that I've seen before include "Manage" , "Many students" , "Unit of time" , "Pupil group" , "Time for earth to go round sun" .)