Happens to be over ten? Apparently not (3)
I believe the answer is:
six
'apparently not' is the definition.
I can't tell whether this defines the answer.
'happens to be over ten?' is the wordplay.
'happens' becomes 'is' (to be can mean to happen).
'to be over' says the letters should be written backwards.
'ten?' becomes 'x' (roman numeral).
'is' in reverse letter order is 'si'.
'si'+'x'='SIX'
(Other definitions for six that I've seen before include "Maximum cricket hit" , "Knock for . . . - surprise or defeat" , "Number of US moon landings" , "Half a dozen" , "Airborne boundary hit" .)