Unemployed Ian didn't like exertion initially (4)
I believe the answer is:
idle
'unemployed' is the definition.
(associated in meaning)
'ian didn't like exertion initially' is the wordplay.
'initially' indicates taking the first letters.
The first letters of 'ian didnt like exertion' is 'IDLE'.
(Other definitions for idle that I've seen before include "Still" , "'Lazy, not doing anything (4)'" , "Indolent" , "out of a job" , "At leisure" .)