A noun "nettle" represents various species of plants, including urtica dioica, urtica incisa, laportea canadensis, dendrocnide, urera baccifera, urtica ferox, eucnide spp., and dendrocnide photinophylla, which have foliage covered with stinging, mildly poisonous hairs causing an instant rash.

A noun "nettle" represents certain plants that have spines or prickles, including ball nettle, bull nettle, silver-leaf nettle, white horse-nettle, western horse-nettle, robust horse-nettle, horse-nettle, and celtis (hackberry).

A type of plant that includes certain non-stinging plants in the family lamiaceae, as well as other plants such as false nettle, flame nettle, hedge nettle, hemp nettle, horse nettle, and nilgiri nettle.

Loosely, anything which causes a similarly stinging rash, such as a jellyfish or sea nettle.

(transitive) Of the nettle plant and similar physical causes, to sting, causing a rash in someone.

(transitive, figuratively) To pique, irritate, vex or provoke.