thorn

noun

A stiff, woody, rigid process on a plant; specifically, a short, indurated, sharp-pointed, and leafless branch developed from a bud (replacing the growing point) in a manner typical to a leafy branch. In some plants the development of thorns and subsequent suppression of the growing points may be a response to dry conditions. Examples are the thorns of gorse and hawthorn. Sometimes applied to any structure resembling a true thorn. Cf. prickle, spine.