Corrected oval with one instrument (5)
I believe the answer is:
viola
'instrument' is the definition.
(viola is a kind of instrument)
'corrected oval with one' is the wordplay.
'corrected' indicates anagramming the letters.
'with' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'oval' is an anagram of 'vola'.
'vola' placed around 'i' is 'VIOLA'.
(Other definitions for viola that I've seen before include "Page" , "Achievement" , "Large fiddle" , "Sebastian's sister" , "Stringed instrument tuned lower than a violin" .)