Exhausted, working in dread (7)
I believe the answer is:
drained
'exhausted' is the definition.
(similar in meaning)
'working in dread' is the wordplay.
'working' indicates anagramming the letters.
'in'+'dread'='indread'
'indread' is an anagram of 'DRAINED'.
(Other definitions for drained that I've seen before include "empty" , "Tired" , "Deprived of strength" , "Exhausted" , "spent" .)