A noble expected to welcome knight (4)
I believe the answer is:
duke
'a noble' is the definition.
(duke is a kind of noble)
'expected to welcome knight' is the wordplay.
'expected' becomes 'due' (I've seen this before).
'to welcome' means one lot of letters goes inside another (in sense of 'inviting in').
'knight' becomes 'k' (**).
'due' enclosing 'k' is 'DUKE'.
(Other definitions for duke that I've seen before include "Highest ranked British peer" , "Nickname of John Wayne" , "Highest ranking British peer" , "Highest rank of British peer" , "High hereditary title in Britain" .)