Thin, emaciated (4)
I believe the answer is:
bony
This clue is a double definition.
'thin' is the first definition.
(similar in meaning)
'emaciated' is the second definition.
(synonyms)
(Other definitions for bony that I've seen before include "Osseous" , "With skeleton showing through" , "[GAUNT] ?" , "Skeletal" , "Angular" .)