Picaroon picked up cat hair (7)
I believe the answer is:
eyelash
'hair' is the definition.
(I know that eyelash is a type of hair)
'picaroon picked up cat' is the wordplay.
'picaroon' becomes 'I' (where the crossword setter is 'Picaroon').
'picked up' shows a homophone (sound like).
'cat' becomes 'lash' (I've seen this before).
'i' sounds like 'eye'.
'eye'+'lash'='EYELASH'
(Other definitions for eyelash that I've seen before include "Hairs on lid edge" , "batter" , "Short curved hair" , "Say heel (anag)" , "Row of facial hairs" .)