Other parent presumably also missing opera (5)
I believe the answer is:
norma
'presumably also missing opera' is the definition.
'norma' can be an answer for 'opera' (I've seen this in another clue). I'm not sure about the 'presumably also missing' bit.
'other parent' is the wordplay.
'other' becomes 'nor' (I can't explain this - if you can you should give a lot more credence to this answer).
'parent' becomes 'ma' (ma can mean mum or mother).
'nor'+'ma'='NORMA'
Can you help me to learn more?
(Other definitions for norma that I've seen before include "musical work" , "Roman (anag) - girl's name" , "Girl" , "Eponymous woman of opera" , "Marilyn was properly one" .)