Tended to break asunder after the start (6)
I believe the answer is:
nursed
'tended to' is the definition.
(I've seen this in another clue)
'break asunder after the start' is the wordplay.
'break' indicates an anagram.
'after the start' means to remove the first letter.
'asunder' with its first letter taken off is 'sunder'.
'sunder' with letters rearranged gives 'NURSED'.
(Other definitions for nursed that I've seen before include "Took care of the sick" , "Cared for the ill" , "Tended to the sick, cared for" , "Carefully treated" , "Took care of while ill" .)