Chevalier vs. cavalier
The French words 'chevalier' and 'cavalier' both relate to horsemen, but they have distinct meanings and uses in modern French.
Chevalier
'Chevalier' refers to a knight or a member of certain orders of knighthood. It often carries a noble or honorable connotation.
Le chevalier en armure brillante défendait le château.
(The knight in shining armor defended the castle.)
Il a été fait Chevalier de la Légion d'honneur.
(He was made a Knight of the Legion of Honor.)
Cavalier
'Cavalier' generally means a horseman or rider. It can also refer to a cavalryman in military contexts.
Le cavalier monte son cheval avec grâce.
(The rider mounts his horse gracefully.)
Les cavaliers de l'armée ont paradé dans la rue principale.
(The army's cavalrymen paraded down the main street.)
Summary
While 'chevalier' typically refers to a knight or an honorable title, 'cavalier' is a more general term for a horseman or rider. 'Chevalier' has historical and noble connotations, while 'cavalier' is used in both military and civilian contexts for anyone who rides a horse.