Rung number? Most of class engaged, possibly (6,3)
I believe the answer is:
spoken for
'engaged possibly' is the definition.
(spoken for can mean in a relationship)
'rung number? most of class' is the wordplay.
'rung' becomes 'spoke' (synonyms).
'number?' becomes 'n' (n can represent any number).
'most of' means to remove the last letter.
'class' becomes 'form' (synonyms).
'form' with its final letter taken away is 'for'.
'spoke'+'n'+'for'='SPOKEN FOR'
(Other definitions for spoken for that I've seen before include "having been a representative" , "Not a single" , "Already claimed" , "Engaged" , "Unavailable (as a partner)" .)