Plump for something schmaltzy! (3)
I believe the answer is:
fat
'plump' is the definition.
(synonyms)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for fat that I've seen before include "Adipose tissue" , "eg Lard" , "Portly" , "Excess body weight" , "Cooking grease" .)