Keen to take in one nearly new feature (9)
I believe the answer is:
lineament
'feature' is the definition.
(I know that feature can be written as lineament)
'keen to take in one nearly new' is the wordplay.
'keen' becomes 'lament' (keen can mean to wail with grief).
'to take in' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'nearly' means to remove the last letter.
'new' with its last letter taken away is 'ne'.
'i'+'ne'='ine'
'lament' enclosing 'ine' is 'LINEAMENT'.
(Other definitions for lineament that I've seen before include "(Facial) feature" , "Distinctive character" , "distinguishing feature" .)