Gloomy woman's mother, 50 (6)
I believe the answer is:
dismal
'gloomy' is the definition.
(I know that gloomy can be written as dismal)
'woman's mother 50' is the wordplay.
'woman's' becomes 'di's' (Di is short for Diana).
'mother' becomes 'ma' (Ma is another word for mother or mum).
'50' becomes 'l' (Roman numeral).
'dis'+'ma'+'l'='DISMAL'
(Other definitions for dismal that I've seen before include "Gloomy, dreary" , "Lugubrious" , "Wretched" , "Dreary; awful" , "pitifully bad" .)