Drab robes, possibly (5)
I believe the answer is:
sober
'drab' is the definition.
(thesaurus)
'robes possibly' is the wordplay.
'possibly' indicates anagramming the letters.
'robes' with letters rearranged gives 'SOBER'.
(Other definitions for sober that I've seen before include "Unintoxicated" , "Serious - sombre" , "Dignified and serious" , "Dry - dull" , "Dignified and sombre in manner: dry" .)