Fibre shown by female, one getting keen (8)
I believe the answer is:
filament
'fibre' is the definition.
(filament is a kind of fibre)
'female one getting keen' is the wordplay.
'female' becomes 'f' (abbreviation).
'one' becomes 'i' (Roman numeral).
'getting' says to put letters next to each other.
'keen' becomes 'lament' ('lament' can be a synonym of 'keen'**).
'f'+'i'+'lament'='FILAMENT'
'shown by' is the link.
(Other definitions for filament that I've seen before include "Thread-like object" , "Wire in incandescent bulb" , "one can become incandescent" , "One may be incandescent" , "Slender fibre or wire" .)