Drab and dull old woman depresses you, first of all (5)
I believe the answer is:
dowdy
'drab' is the definition.
(I've seen this before)
'dull old woman depresses you first of all' is the wordplay.
'first of all' suggests taking the first letters.
The first letters of 'dull old woman depresses you' is 'DOWDY'.
'and' is the link.
(Other definitions for dowdy that I've seen before include "Frumpish" , "Lacking chic" , "Drab" , "Unsmart" , "Drably dressed" .)