Started work on an exceptional need (6)
I believe the answer is:
opened
'started' is the definition.
(opening is a kind of starting)
'work on an exceptional need' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'an exceptional' indicates anagramming the letters (an unusual or exceptional ordering of the letters).
'need' is an anagram of 'ened'.
'op'+'ened'='OPENED'
(Other definitions for opened that I've seen before include "Unfastened or moved a barrier" , "Turned key to permit entry, or removed lid" , "Took the lid off" , "Afforded access" , "Gave access by unlocking" .)