Unusual chemise and odd robe regularly stained (10)

'stained' is the definition.
(synonyms)

'unusual chemise and odd robe regularly' is the wordplay.
'unusual' is an anagram indicator.
'and' is a charade indicator (letters next to each other).
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'odd'+'robe'='oddrobe'
The alternate letters of 'oddrobe' are 'drb'.
'chemise' put after 'drb' is 'drbchemise'.
'drbchemise' is an anagram of 'BESMIRCHED'.