A cornet is a brass wind instrument similar to a trumpet but smaller. The word was originally a diminutive of the Old French corn, meaning horn, so it translates roughly to little horn. Coronet refers to (1) a small crown worn by princes and princesses, and (2) the upper margin or a horse’s hoof. It, too, comes from Old French, originating as a diminutive of corone (meaning crown).
Examples
His father is also a trombone player, but Luscombe chose the cornet as his first instrument. [State Gazette]
A stunning soprano cornet solo performed by 13-years-old Thomas Jordan was one highlights of the victory. [Leigh Journal]
Katherine is doomed as soon as she accepts her coronet. She is no match for the courtiers around her, especially the king’s lusty and lustful groom Culpepper. [Boston Herald]
The entire has been troubled by a cut to the coronet of his right foreleg sustained in the Ashburton Flying Stakes when he lost a plate. [Otago Daily Times]