Masculine side backed denial by meeting’s end (4)
I believe the answer is:
yang
'masculine side' is the definition.
(I've seen this in another clue)
'backed denial by meeting's end' is the wordplay.
'backed' says the letters should be written in reverse.
'denial' becomes 'nay' (nay is a kind of denial).
'by' means one lot of letters go next to another.
'end' suggests the final letters.
The final letter of 'meeting' is 'g'.
'nay' back-to-front is 'yan'.
'yan'+'g'='YANG'
(Other definitions for yang that I've seen before include "positive force" , "philosophical principle" , "Positive element in traditional Chinese philosophy" , "Complement of yin" , "Yin's counterpart" .)