Stock a line in fashionable style (5)
I believe the answer is:
talon
'stock' is the definition.
(I've seen this before)
'a line in fashionable style' is the wordplay.
'line' becomes 'l' (used when specifying particular lines from a poem).
'in' means one lot of letters goes inside another.
'fashionable style' becomes 'ton'.
'a'+'l'='al'
'al' inserted within 'ton' is 'TALON'.
(Other definitions for talon that I've seen before include "hunting hook" , "Raptor's claw" , "Tonal (anag.)" , "Bird of prey's claw" , "Eg, an eagle's claw" .)