Old-fashioned duke had died (5)
I believe the answer is:
dated
'old-fashioned' is the definition.
(dated can mean old-fashioned)
'duke had died' is the wordplay.
'duke' becomes 'd' (abbreviation).
'had' becomes 'ate' ('have' can mean 'eat').
'died' becomes 'd' (abbreviation next to the year of someone's death).
'd'+'ate'+'d'='DATED'
(Other definitions for dated that I've seen before include "Archaic; took out" , "old > saw" , "Went steady" , "Met socially by arrangement" , "not without romantic engagements" .)