thorn (plural thorns)
1. A sharp protective spine of a plant.
2. Any shrub or small tree that bears thorns. the white thorn; the cockspur thorn
3. (figuratively) That which pricks or annoys; anything troublesome.
4. A letter of the Latin alphabet borrowed by Old English from the futhark to represent a dental fricative, then not distinguished from eth, but in modern use (in Icelandic and other languages, but no longer in English) used only for the voiceless dental fricative found in English thigh.