Baby lettuce plant (6)
I believe the answer is:
cosset
'baby' is the definition.
('cosset' can be a synonym of 'baby')
'lettuce plant' is the wordplay.
'lettuce' becomes 'cos' (cos lettuce is a kind of lettuce).
'plant' becomes 'set'.
'cos'+'set'='COSSET'
(Other definitions for cosset that I've seen before include "Protect overindulgently" , "Baby" , "Care for overindulgently" , "Care for and protect" , "pet" .)