Dinictis was named by American paleontologist Joseph Leidy in 1854. Its type is Dinictis felina. It was assigned to Nimravidae by Leidy (1854); and to Nimravinae by Flynn and Galiano (1982), Bryant (1991) and Martin (1998).
Dinictis had a sleek body 1.1 metres (3.6 ft) long, short legs 0.6 metres (2.0 ft) high with only incompletely retractable claws, powerful jaws, and a long tail. It was very similar to its close relative, Hoplophoneus. The shape of its skull is reminiscent of a felid skull rather than of the extremely short skull of the Machairodontinae. Compared with those of the more recent machairodonts, its upper canines were relatively small, but they nevertheless distinctly protruded from its mouth. Below the tips of the canines, its lower jaw spread out in the form of a lobe.
Dinictis walked plantigrade (flat-footed), unlike modern felids. It looked like a small leopard and evidently its mode of life was similar to that of a leopard. It was probably not so particular about its food as its descendants, since the reduction of its teeth was still in the early stages and Dinictis had not forgotten how to chew. Despite this, in its own environment it would have been a powerful predator.