It's more trouble going topless (5)
I believe the answer is:
other
'it's more' is the definition.
(synonyms)
'trouble going topless' is the wordplay.
'trouble' becomes 'bother' (synonyms).
'going topless' means to remove the first letter.
'bother' with its first letter taken off is 'OTHER'.
(Other definitions for other that I've seen before include "Second" , "Very unusual" , "else!" , "Not the one mentioned" , "Remaining" .)