Very old, battered tin can pierced by end of knife (7)
I believe the answer is:
ancient
'very old' is the definition.
(I've seen this before)
'battered tin can pierced by end of knife' is the wordplay.
'battered' indicates anagramming the letters.
'pierced by' means one lot of letters goes inside another (some letters pierce a hole in others).
'end of' says to take the final letters.
The final letter of 'knife' is 'e'.
'tin'+'can'='tincan'
'tincan' with letters rearranged gives 'ancint'.
'ancint' enclosing 'e' is 'ANCIENT'.
(Other definitions for ancient that I've seen before include "from Aristophanes' time" , "Veteran" , "Nice tan (anag.)" , "Very old, belonging to times long ago" , "Very old, like the poetic mariner" .)