The correct answer is (B) Single flower worn in a lapel buttonhole; a flower worn on the lapel, or in the buttonhole of a lapel, usually by a man. Also, a small floral sprig or spray of flowers worn in a buttonhole.

Boutonniere comes from French boutonniere (buttonhole), Middle French bouton (button).

Examples of use:

• The prime minister always wore a boutonniere in the lapel of his suit.
• He usually selected a red rose for his boutonniere.