Unmarried person going topless? Seemingly not! (9)
I believe the answer is:
singleton
'seemingly not' is the definition.
I can't tell whether this defines the answer.
'unmarried person going topless?' is the wordplay.
'unmarried' becomes 'single-' (similar in meaning).
'person' becomes 'to' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'going' becomes 'on' (both can mean functioning or activated).
'topless?' means to remove the first letter (I've seen 'topless' mean this).
'on' with its first letter taken off is 'n'.
'single'+'to'+'n'='SINGLETON'
Can you help me to learn more?
(Other definitions for singleton that I've seen before include "lonely heart, perhaps" , "Bachelor maybe" , "one without a mate?" , "Eg lonely heart" , "spinster or bachelor?" .)