Following diversion, ultimately become very gloomy (8)
I believe the answer is:
funereal
'gloomy' is the definition.
('funereal' can be a synonym of 'gloomy')
'following diversion ultimately become very' is the wordplay.
'following diversion' becomes 'fun' (fun is a kind of diversion. I am not sure about the 'following' bit.**).
'ultimately' says to take the final letters.
'very' becomes 'real' ('real' can be similar in meaning to 'very').
The last letter of 'become' is 'e'.
'fun'+'e'+'real'='FUNEREAL'
Can you help me to learn more?
(Other definitions for funereal that I've seen before include "Of the ritual of the dead" , "Gloomy" , "Of sombre character" .)