Model style mostly followed by one in five (9)
I believe the answer is:
mannequin
'model' is the definition.
(I know that model can be written as mannequin)
'style mostly followed by one in five' is the wordplay.
'style' becomes 'manner' (synonyms).
'mostly' means to remove the last letter (most but not all of the word).
'followed by' means one lot of letters go next to another.
'one in five' becomes 'quin' (short for quintuplet).
'manner' with its final letter taken away is 'manne'.
'manne'+'quin'='MANNEQUIN'
(Other definitions for mannequin that I've seen before include "Shop's dummy" , "Display dummy" , "Life-size dummy for displaying clothes" , "fashion model" , "Dummy figure" .)