Vital one shows the claw (5)
I believe the answer is:
talon
'the claw' is the definition.
(talon is a kind of claw)
'vital one shows' is the wordplay.
'shows' indicates a hidden word.
'TALON' is hidden within 'vital one'.
(Other definitions for talon that I've seen before include "a gripping one" , "Bird of prey's claw" , "Large claw" , "hunting hook" , "The stock" .)