Impassive, unemotional (6)
I believe the answer is:
stolid
This clue is a double definition.
'impassive' is the first definition.
(I know that impassive can be written as stolid)
'unemotional' is the second definition.
(similar in meaning)
(Other definitions for stolid that I've seen before include "Impassive, unemotional" , "Strongly built" , "Not excitable, doesn't show emotion" , "Not excitable or emotional" , "Hard to move" .)