Dressed, perhaps mostly for bed (5)
I believe the answer is:
robed
'dressed' is the definition.
(synonyms)
'perhaps mostly for bed' is the wordplay.
'perhaps' indicates an anagram.
'mostly' means to remove the first letter (1).
'for' with its first letter taken away is 'or'.
'or' anagrammed gives 'ro'.
'ro'+'bed'='ROBED'
(Other definitions for robed that I've seen before include "Wearing judge's garments" , "Dressed" , "Attired" , "In a long garment" .)