Chap with key to crypt (4)
I believe the answer is:
tomb
'crypt' is the definition.
(I've seen this in another clue)
'chap with key' is the wordplay.
'chap' becomes 'tom' (a man's name).
'with' is a charade indicator (letters next to each other).
'key' becomes 'b' (eg B major, musical key).
'tom'+'b'='TOMB'
'to' acts as a link.
(Other definitions for tomb that I've seen before include "grave situation" , "Burial-vault" , "Crypt or grave" , "Large vault" , "Sepulchre" .)