Chap, born one of large family, is a dummy (9)
I believe the answer is:
mannequin
'dummy' is the definition.
(I know that mannequin is a type of dummy)
'chap born one of large family' is the wordplay.
'chap' becomes 'man' (chap can mean a man).
'born' becomes 'ne' ('born' in French - used to indicate a birth name).
'one of large family' becomes 'quin' (short for quintuplet).
'man'+'ne'+'quin'='MANNEQUIN'
'is a' acts as a link.
(Other definitions for mannequin that I've seen before include "Dummy figure" , "fashion model" , "Life-size dummy for displaying clothes" , "Display dummy" , "Shop's dummy" .)