Passing a helper needing more clothing models (9)
I believe the answer is:
ephemeral
'passing' is the definition.
(I know that passing can be written as ephemeral)
'a helper needing more clothing models' is the wordplay.
'needing' is a charade indicator (letters next to each other).
'clothing' suggests removing the centre.
'models' indicates anagramming the letters.
'more' with its middle taken out is 'me'.
'a'+'helper'+'me'='ahelperme'
'ahelperme' anagrammed gives 'EPHEMERAL'.
(Other definitions for ephemeral that I've seen before include "Lasting only briefly" , "short term gain" , "A mere help (anag) - short-lived" , "Having only brief existence" , "Short lived" .)