Mezoneuron kavaiense is a shrub or tree, typically reaching heights between 4 to 10 meters. It possesses a sturdy structure with dark gray, thick bark that is rough and divides into rectangular or oblong plates. Mature plants possess trunk diameters reaching up to 30 cm. The leaves are compound, arranged alternately along the stem, with 1–5 pairs of pinnae per leaf and 4–8 pairs of oblong leaflets per pinna, which are roughly sub-opposite. The leaflets measure 2–5 cm in length and 1–2 cm in width, featuring a subtruncate, usually emarginate apex and an oblique, rounded base. The lower surfaces and midrib are covered in a rusty tomentose texture. Each leaf is borne on a petiole, and the plant features small, wart-like subulate stipules about 2 mm in length. The flowers are organized in terminal racemes measuring 5–15 cm long. These racemes and their pedicels, which are 2.5–4 cm long and jointed in the upper part, are covered in rusty, wooly hairs. The flowers are distinct and bisexual, spanning up to 20 mm in diameter without bracteoles. The calyx is pink to rose, with upper and lateral lobes measuring 10–13 mm long and a lower concave lobe extending 16–18 mm. The petals are rose, darkening to red at the margins, with varied shapes including obcordate and obovate forms, and the stamens are exserted with reddish pubescent filaments and red anthers. There are ten distinct stamens of alternating lengths, and the ovary is superior with 3–5 ovules and a glabrous, incurved style. The fruits are indehiscent, strongly flattened pods that are obovate-oblong, measuring 9–13 cm in length and 4.5–6 cm in width, with a distinctive glaucous appearance and a longitudinal wing about 0.9–1.3 cm wide near the upper margin. It contains 2–4 transversely arranged pale brown, ovoid, and flattened seeds, each 17–19 mm long and 16–18 mm wide. It is found in dry to mesic forests between  80–920 meters.