Essays by one in a state of rest (5)
I believe the answer is:
tries
'essays' is the definition.
(essay can mean to try or attempt something)
'one in a state of rest' is the wordplay.
I cannot quite see how this works, but
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
an anagram of 'rest' is 'tres' which is within the remaining letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'by' acts as a link.
Can you help me to learn more?
(Other definitions for tries that I've seen before include "Attempts" , "Scoring moves in rugby" .)