thorn

In botany, a thorn is a sharp, pointed projection that arises from a plant stem. Thorns are typically modified branches that include wood and vascular tissue, and they can be simple spines or branched structures. They differ from spines, which are modified leaves or leaf parts, and from prickles, which are outgrowths of the epidermis. Thorns are a common defense against herbivores and can vary in size, persistence, and mechanism of formation across plant families. Examples include the long spines of cacti, the thorns on many citrus trees, and the branched thorns of hawthorns and acacias. Some thorns are deciduous while others persist for years; in some species, thorns may regenerate after damage.

In writing, thorn refers to the letter Þ/þ, known as thorn, used in Old English and Icelandic to represent the sounds /θ/ or /ð/. The letter survived in Icelandic but disappeared from modern English, replaced by 'th'. The name thorn is used to describe that character in historical and linguistic contexts.

Beyond biology and linguistics, Thorn is used as a surname and as a place name. There are people with the surname Thorn and places named Thorn in various countries, including a town in the Netherlands. The term also appears in literature and cultural references as a proper noun.