Appearance of this person in pieces (4)
I believe the answer is:
mien
'appearance' is the definition.
(I've seen this in another clue)
'this person in pieces' is the wordplay.
'this person' becomes 'I'.
'in' means one lot of letters goes inside another.
'pieces' becomes 'men' (man can mean a chess piece).
'i' inserted inside 'men' is 'MIEN'.
'of' is the link.
(Other definitions for mien that I've seen before include "person's look" , "(One's) manner, bearing" , "Person's bearing" , "Appearance is strangely mine" , "A person's demeanour" .)