Canavalia hawaiiensis is a perennial climber with twining branches. The leaves are compound and alternate. The leaflets are ovate to broadly ovate, elliptic to broadly elliptic, or sometimes suborbicular, measuring (5–)8–13 cm long and (3–)4–8.5(–10) cm wide. The apex of the leaflets is short-acuminate or sometimes acuminate, while the base ranges from truncate to cuneate. The upper surfaces of the leaflets are sparsely to moderately or rarely densely appressed pubescent, typically becoming glabrate with age, and the lower surfaces are densely or sometimes moderately appressed pubescent; leaflets are chartaceous. The margins of the leaflets are entire. The leaves are petiolate with small, caducous stipules and minute leaflet stipels. The flowers usually number 8–15(–20) in axillary pseudoracemes 4–16 cm long. The flowers are papilionaceous (resembling a butterfly) with caducous bracteoles. The calyx is 18–25 mm long, moderately to densely appressed pubescent, with a smooth, strongly concave upper edge and an apiculate apex. The upper lip of the calyx is 11–14 mm long with two lobes connate except in the distal 3 mm, and the lowest lobe is lanceolate, 4–6 mm long. The calyx is bilabiate and 5-lobed. The corolla is a dark carmine with a standard with a white spot at its base and yellow to white streaks toward the base, measuring 30–38 mm long. The wing petals are 40–41 mm long, and the keel petals are approximately 45 mm long. It has ten stamens; the upper stamen is distinct at the base and loosely adheres to the other nine up to the middle, which are connate into a tube. The ovary is superior and stipitate with 5–20 ovules; the style is incurved and glabrous; the stigma is small and terminal. The fruits are compressed pods, measuring (12–)16–28 cm long and 2.5–3.7 cm wide, with a moderately appressed pubescent surface that becomes less so with age. Each valve of the pod features an inconspicuous sutural ridge and an additional longitudinal ridge 1–1.5 mm below the upper suture. The seeds are dark reddish-brown, oblong-elliptic, strongly compressed, and measure 20–24 mm long and 14–16 mm wide. The hilum is 10–13 mm long. It occurs in dry to diverse mesic forests between 120-1,220 meters.