Small starter of duck and shrimp (4)
I believe the answer is:
weed
'shrimp' is the definition.
(both can mean a weak or puny person)
'small starter of duck' is the wordplay.
'small' becomes 'wee' (Scottish term for small).
'starter of' suggests taking the first letters.
The first letter of 'duck' is 'd'.
'wee'+'d'='WEED'
'and' is the link.
(Other definitions for weed that I've seen before include "Troublesome plant" , "Marijuana (slang)" , "dope" , "Went" , "gone!" .)