(1):

(n.) Fig.: That which pricks or annoys as a thorn; anything troublesome; trouble; care.

(2):

(v. t.) To prick, as with a thorn.

(3):

(n.) A hard and sharp-pointed projection from a woody stem; usually, a branch so transformed; a spine.

(4):

(n.) Any shrub or small tree which bears thorns; especially, any species of the genus Crataegus, as the hawthorn, whitethorn, cockspur thorn.

(5):

(n.) The name of the Anglo-Saxon letter /, capital form /. It was used to represent both of the sounds of English th, as in thin, then. So called because it was the initial letter of thorn, a spine.