The honey locust (Gleditsia triacanthos), also known as the thorny locust or thorny honeylocust, is a deciduous tree in the family Fabaceae, native to central North America where it is mostly found in the moist soil of river valleys. Honey locust trees are highly adaptable to different environments, and the species has been introduced worldwide. Outside its natural range it can be an aggressive, damaging invasive species.

The honey locust, Gleditsia triacanthos, can reach a height of 20–30 m (65–100 ft). They exhibit fast growth, but live a medium life span, as long as 125 years. The leaves are pinnately compound on older trees but bipinnately compound on vigorous young trees. The leaflets are 1.4–3.6 cm (1⁄2–1+1⁄2 in) long when compound and very slightly smaller when bipinnate. The leaves are green in summer and turn yellow in autumn in shades ranging from cream and tan to golden yellow. Honey locusts leaf out relatively late in spring, but generally slightly earlier than the black locust (Robinia pseudoacacia).

The strongly scented flowers appear in late spring. Each cluster is a raceme 3–7 centimeters long with many tiny greenish-yellow to greenish-white flowers. The trees are polygamous-dioecious: many trees have only pollen producing flowers or seed producing flowers (strictly dioecious), but some will have both types of flowers in separate clusters, though usually one type will predominate.

The fruit of the honey locust is a flat pod (a legume) that matures in early autumn and is often twisted or curved. The average size of the pods is 7–35 cm (3–14 in) long and 1.5–3 cm (1⁄2–1+1⁄4 in) wide. Once ripe the pod will contain as many as twenty dark brown oval seeds, each about 2 cm (1 in) long. Surrounding the seeds is a soft, gooey pulp with a slightly sweet flavor. Pods may be produced from mid-September through mid-October in its native habitat.

Honey locusts commonly have thorns 6–10 cm (2+1⁄2–4 in) long growing out of the branches and trunk, some reaching lengths of 20 cm (8 in); these may be single, or branched into several points, and commonly form dense clusters. The thorns are modified branches and occasionally sprout leaves. Thornless forms are occasionally found growing wild and are commonly available as nursery plants.

Honey locust was given its scientific name of Gleditsia triacanthos by Carl Linnaeus in 1753 in his book Species Plantarum. Its taxonomic history is quite complex with a total of 41 names that are taxonomic synonyms including five botanical forms, fourteen varieties, and twenty-two species. Included in its synonyms by Plants of the World Online, World Flora Online, and the USDA Natural Resources Conservation Service PLANTS database is the subordinate taxon Gleditsia triacanthos var. inermis. However, this scientific name is still found in gardening websites and books to distinguish thornless trees.

Hybridization of honey locust with water locust (Gleditsia aquatica) has been reported.

The genus Gleditsia is named in honor of Johann Gottlieb Gleditsch, the director of what has become the Berlin Botanical Garden and Botanical Museum. The species name is derived from Greek and means "three thorns". The common name most often used for the species is "honey locust". This name comes from the slightly sweet pulp that surrounds the seeds in the tree's pods and their resemblance to the pods of the carob or "locust tree" from the Middle East. Honey locust is also used for the genus as a whole or for other species in it. The first recorded use of the name was in 1709 by John Lawson in his account A New Voyage to Carolina. In the late 1800s honey locust was sometimes used as an alternate name in localized areas for other species such as for mesquit (Prosopis juliflora) in Texas and New Mexico, for black locust (Robinia pseudoacacia) in Minnesota, and for clammy locust (Robinia viscosa) in New York and New Jersey. Variants on this name include "common honey locust", "honeylocust", and "thornless honey locust".