A king during trial, not moving (2,4)
I believe the answer is:
at rest
'not moving' is the definition.
(I've seen this before)
'a king during trial' is the wordplay.
'king' becomes 'r' (r is abbreviation for rex).
'during' indicates putting letters inside.
'trial' becomes 'test' ('test' can be a synonym of 'trial').
'r' going into 'test' is 'trest'.
'a'+'trest'='AT REST'
(Other definitions for at rest that I've seen before include "Not moving, free from anxiety" , "Not moving, free from trouble - maybe dead" , "calm" , "late" , "In relaxed state, perhaps dead" .)