Stand a trainee at ease (5)
I believe the answer is:
easel
'stand' is the definition.
(easel is a kind of stand)
'a trainee at ease' is the wordplay.
'a trainee' becomes 'l'.
'at' means one lot of letters go next to another (I've seen this in other clues).
'l' put after 'ease' is 'EASEL'.
(Other definitions for easel that I've seen before include "supporter of the arts" , "Tripod supporting a canvas" , "Lease it out to the artist" , "Stand used by artists" , "Board stanchion" .)