Botany A modified branch in the form of a sharp, woody spine.
Botany Any of various shrubs, trees, or woody plants bearing sharp, woody spines.
Any of various sharp, spiny protuberances; a prickle.
One that causes sharp pain, irritation, or discomfort: He is a thorn in my side.
The runic letter þ originally representing either sound of the Modern English th, as in the and thin, used in Old English and Middle English manuscripts.