Rise firm to start or represent (5,3)
I believe the answer is:
stand for
'represent' is the definition.
(standing for is a kind of representing)
'rise firm to start or' is the wordplay.
'rise' becomes 'stand' (I've seen this before**).
'to start' indicates taking the first letters.
The first letter of 'firm' is 'f'.
'stand'+'f'+'or'='STAND FOR'
(Other definitions for stand for that I've seen before include "Represent or tolerate" , "Signify" , "champion" , "Represent - in upright posture?" , "Represent or put up with" .)