Monarch once did career officer's commissions (7)
I believe the answer is:
errands
'commissions' is the definition.
(I've seen this in another clue)
'monarch once did career officer's' is the wordplay.
'monarch once' becomes 'ER' (Elizabeth Regina, ie Queen Elizabeth).
'did career' becomes 'ran' (to career can mean to run out of control).
'officer's' becomes 'ds' (I can't justify this - if you can you should give a lot more credence to this answer).
'er'+'ran'+'ds'='ERRANDS'
Can you help me to learn more?
(Other definitions for errands that I've seen before include "Darners (anag.)" , "Task-oriented trips" , "Short journeys" , "shopping trips" , "Delivery journeys" .)