Part of foot -- a long claw (5)
I believe the answer is:
talon
'part' is the definition.
(talon is a kind of part)
'of foot a long claw' is the wordplay.
'of' indicates the answer is hidden within the clue.
'TALON' can be found hidden inside 'foot a long claw'.
(Other definitions for talon that I've seen before include "Holding part of flier" , "Sharp hooked claw" , "Eg, an eagle's claw" , "Tonal (anag.)" , "Bird of prey's claw" .)