A day regarded as well fixed (7)
I believe the answer is:
moneyed
'well fixed' is the definition.
(thesaurus)
'a day regarded' is the wordplay.
'a day' becomes 'mon'.
'regarded' becomes 'eyed' (I've seen this in other clues).
'mon'+'eyed'='MONEYED'
'as' acts as a link.
(Other definitions for moneyed that I've seen before include "Mo' needy? (Anag)" , "rolling in it" , "Rich" , "Having means" , "Well-to-do" .)