Relax concerning attitude (6)
I believe the answer is:
repose
'relax' is the definition.
'concerning attitude' is the wordplay.
'concerning' becomes 're'.
'attitude' becomes 'pose' (I've seen this before**).
're'+'pose'='REPOSE'
(Other definitions for repose that I've seen before include "Lie at rest" , "Rest - tranquillity" , "place" , "Relaxation" , "peace" .)