One irritated by study and run down (10)
I believe the answer is:
denigrated
'run down' is the definition.
The answer and definition are not the same part of speech. However, adjectives and past participle verbs can sometimes mean the same thing.
'one irritated by study' is the wordplay.
'one' becomes 'i' (Roman numeral).
'irritated' becomes 'grated' (grating is a kind of irritating).
'by' means one lot of letters go next to another.
'study' becomes 'den' (term for a study or office).
'i'+'grated'='igrated'
'igrated' after 'den' is 'DENIGRATED'.
'and' acts as a link.
Can you help me to learn more?
(Other definitions for denigrated that I've seen before include "belittled" , "ran down" .)