Stand a trainee at ease (5)
I believe the answer is:
easel
'stand' is the definition.
(stand for an artist's canvas)
'a trainee at ease' is the wordplay.
'a trainee' becomes 'l' (as in an L-plate for a learner driver).
'at' is a charade indicator (letters next to each other) (I've seen this in other clues).
'l' 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" .)