Poet initially unappreciated in a study (5)
I believe the answer is:
auden
'poet' is the definition.
(WH Auden, 1907-1973)
'initially unappreciated in a study' is the wordplay.
'initially' says to take the initial letters.
'in' indicates putting letters inside.
'study' becomes 'den' (term for a study or office).
The initial letter of 'unappreciated' is 'u'.
'a'+'den'='aden'
'u' placed inside 'aden' is 'AUDEN'.
(Other definitions for auden that I've seen before include "W.H. --, English poet" , "British-born writer" , "20th-century Anglo-American poet" , "Wystan Hugh -, poet" , "W. H. ... (British poet)" .)