Unfamiliar parson, ordinary singer (7)
I believe the answer is:
soprano
'singer' is the definition.
(soprano is a kind of singer)
'unfamiliar parson ordinary' is the wordplay.
'unfamiliar' is an anagram indicator.
'ordinary' becomes 'o' (abbreviation e.g. O-Levels).
'parson' with letters rearranged gives 'sopran'.
'sopran'+'o'='SOPRANO'
(Other definitions for soprano that I've seen before include "High singing voice" , "Isolde, Violetta or 25" , "Singer who aims high" , "Producer of high-pitched sounds" , "chorus girl, perhaps" .)