Husband in essential task (5)
I believe the answer is:
chore
'task' is the definition.
(I know that task can be written as chore)
'husband in essential' is the wordplay.
'husband' becomes 'h' (abbreviation).
'in' indicates putting letters inside.
'essential' becomes 'core' (both can mean very important).
'h' placed within 'core' is 'CHORE'.
(Other definitions for chore that I've seen before include "unwelcome task" , "easy option? Not so!" , "Drudgery" , "Tedious routine task" , "Unpleasant task" .)