Task is blunder also (6)
I believe the answer is:
errand
'task' is the definition.
(an errand is a task or job)
'blunder also' is the wordplay.
'blunder' becomes 'err' (to err is to make a mistake or blunder).
'also' becomes 'and' (both can mean in addition).
'err'+'and'='ERRAND'
'is' is the link.
(Other definitions for errand that I've seen before include "Chore" , "run one" , "Short trip with a mission" , "Job usually involving a short trip" , "Short trip to perform required task" .)