Rapid foxtrot by topless performers (4)
I believe the answer is:
fast
'rapid' is the definition.
(similar in meaning)
'foxtrot by topless performers' is the wordplay.
'foxtrot' becomes 'f' (phonetic alphabet: alpha, bravo, charlie etc.).
'by' means one lot of letters go next to another.
'topless' means to remove the first letter.
'performers' becomes 'cast' (I've seen this before).
'cast' with its initial letter taken off is 'ast'.
'f'+'ast'='FAST'
(Other definitions for fast that I've seen before include "requiring only brief exposure" , "Eat nothing" , "requirement before surgery" , "Unlikely to run" , "Quick; firmly fixed" .)