Yawn, partly concealing a peeve (4)
I believe the answer is:
gape
'yawn' is the definition.
(I know that yawn can be written as gape)
'partly concealing a peeve' is the wordplay.
'partly' indicates the answer is hidden within the clue (part of the clue is used).
'GAPE' is hidden within 'concealing a peeve'.
(Other definitions for gape that I've seen before include "Look with mouth wide open" , "Peer" , "Gawp" , "Look at with wide-open mouth" , "Look in amazement or stupidity" .)