thorn Definition

1. A hard sharp point sticking out from the stem or branch of certain plants.

Thesaurus: barb, prickle, spike.
2. A shrub bearing thorns, especially a hawthorn.
3. A constant irritation or annoyance.

Example: a thorn in one's side
Thesaurus: irritation, annoyance, bane, torment, curse, scourge, torture, affliction, plague.
4. The Old English and Icelandic letter þ, pronounced or in Anglo-Saxon and in Icelandic.