Back to find chest established as the gloomiest (7)
I believe the answer is:
darkest
'gloomiest' is the definition.
('dark' can be similar in meaning to 'gloomy')
'back to find chest established as' is the wordplay.
'back to' says to take the final letters.
'chest' becomes 'ark' (historical term for a chest).
'established as' becomes 'est' (abbreviation. I am not sure about the 'as' bit.).
The last letter of 'find' is 'd'.
'd'+'ark'+'est'='DARKEST'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for darkest that I've seen before include "Most gloomy" , "Most devoid of light" , "Most dim" , "'The . . . . . . . hour comes before the dawn'" , "Gloomiest or blackest" .)