RSTVWXYZ? Not acceptable! (3-1)
I believe the answer is:
non-u
'rstvwxyz?' is the definition.
I can't judge whether this defines the answer.
'not acceptable' is the wordplay.
'not' becomes 'non' (I've seen this in other clues).
'acceptable' becomes 'u' (as in U and non-U speech).
'non'+'u'='NON-U'
Can you help me to learn more?
(Other definitions for non-u that I've seen before include "not liked by the toffs" , "Not socially refined" , "Not characteristic of the upper classes" , "Not socially acceptable" , "Common - noun (anag)" .)