Like Don is extravagantly chivalrous (8)
I believe the answer is:
quixotic
This clue is a double definition.
'like don' is the first definition.
(Don Quixote)
'extravagantly chivalrous' is the second definition.
'is' acts as a link.
(Other definitions for quixotic that I've seen before include "Visionary" , "Absurdly generous or naively romantic" , "Impractically idealistic" , "Like a Cervantes character" , "Extravagantly romantic" .)