Some old boy's mater? (4)
I believe the answer is:
alma
'some old' is the definition.
The definition suggests a singular noun which matches the answer.
'boy's mater?' is the wordplay.
'boy' becomes 'al' ().
'mater?' becomes 'ma' (synonyms).
'al'+'ma'='ALMA'
Can you help me to learn more?
(Other definitions for alma that I've seen before include "dancing girl" , "Essence" , "Battle of the -- was in the Crimean War" , "Loving girl" , "The . . . . Mater is the old school" .)