Brownie brought over by shrink makes you fat (6)
I believe the answer is:
fleshy
'fat' is the definition.
(similar in meaning)
'brownie brought over by shrink' is the wordplay.
'brownie' becomes 'elf' (synonyms).
'brought over' says the letters should be written in reverse.
'by' means one lot of letters go next to another.
'shrink' becomes 'shy' (I've seen this in another clue).
'elf' in reverse letter order is 'fle'.
'fle'+'shy'='FLESHY'
'makes you' is the link.
(Other definitions for fleshy that I've seen before include "voluptuous!" , "Plump and meaty" , "Plump; soft and thick" , "Sarcoid" , "Fat" .)