Strong back or chest (6)
I believe the answer is:
robust
'strong' is the definition.
(similar in meaning)
'back or chest' is the wordplay.
'back' says the letters should be written backwards.
'chest' becomes 'bust' (bust can mean a woman's chest).
'or' back-to-front is 'ro'.
'ro'+'bust'='ROBUST'
(Other definitions for robust that I've seen before include "Athletic" , "Study and durable" , "Hardy and vigorous" , "Strong and healthy" , "Full and rich (wine)" .)