Honey locust is a medium-sized tree with a short, thorny trunk, thorny branches, and a loose, open crown.
Leaves are alternate, compound, 5–10 inches long, with 15–30 leaflets; leaflets ¾–2 inches long, broadest near the base to even throughout; margin entire or sometimes with very small, round teeth; upper surface shiny; lower surface paler, often hairy.
Bark is grayish brown to black, on older trees with grooves deep, narrow, separating into scaly ridges with sides or ends free and curved outward; often bearing heavy, simple or branching spines.
Twigs are greenish or reddish brown, shiny, stout, often zigzag, with solitary or branched spines that are rigid, sharp, straight, shiny, purplish brown, up to 12 inches long.
Flowers May–June; greenish white; male flowers in catkins, female flowers in clusters; found on separate trees or sometimes as a complete flower.
Fruit a dark brown, leathery pod, 6–18 inches long, narrow, flat, twisting at maturity; seeds 6–27, brown, oval, about ½ inch long.