Cyrtandra hawaiensis is a shrub reaching heights between 1–3(–5) meters, featuring stems that are either unbranched or few-branched, with a rounded to angular shape, and a surface that is pubescent with multicellular hairs or become smoother (glabrate) over time. The leaves are arranged in whorls of 3–6 at each node, though typically found in groups of 4, with the leaves at a node being either equal or unequal in size and shape and symmetrical. These leaves range from elliptic–oblanceolate to narrowly oblanceolate or sometimes narrowly elliptic in shape, measuring (8–)12–30(–57) cm in length and (1.3–)3–8(–14.5) cm in width. The leaf apex is long-acuminate to acuminate or occasionally acute, with a long-attenuate base. The leaf surfaces vary in texture, with the upper surfaces typically becoming glabrate and the lower surfaces ranging from glabrate to densely pilose along the veins, particularly in younger leaves from O’ahu. The leaves are thick or occasionally thin, chartaceous to subcoriaceous, and feature serrulate margins with teeth often widely spaced. The flowers appear 1–5 in usually dense, often compound cymes arising from the leaf axils or the few nodes below the leaves. These flowers are perfect and exhibit a zygomorphic calyx that is fusiform in the bud, tipped by a beak 3–17 mm long, and ranges from 15–48 mm long in anthesis. The corolla is usually bilabiate and white, and the tube is narrowly funnelform and curved near the middle. Stamens include two fertile upper stamens and others that are staminodial, with coherent anthers positioned in the throat of the corolla tube. The ovary is superior, glabrous, oblong–ovoid, with a parietal placentation. The fruit is a fleshy or firm berry, white, oblong–ellipsoid, 2–3.8 cm long, often tipped by the persistent stylar beak, containing numerous minute, ellipsoid seeds measuring 0.4–0.5 mm in length with a reticulate surface. It thrives on slopes, in gulch bottoms, along streams within mesic valleys, and mesic to wet forests between 120–700(–1,380) meters.