Fashion line for mannequin (5)
I believe the answer is:
model
'for mannequin' is the definition.
(synonyms)
'fashion line' is the wordplay.
'fashion' becomes 'mode' (synonyms).
'line' becomes 'l' (used when specifying particular lines from a poem).
'mode'+'l'='MODEL'
(Other definitions for model that I've seen before include "Miniature replica" , "clothes horse?" , "Example (on the catwalk?)" , "Example to follow" , "(Person functioning as) example" .)