Neraudia kauaiensis is a shrub that can grow up to 5 meters tall. Its branches are pubescent, with erect or spreading hairs supporting the leaf and flower structures. The leaves are simple and alternate with elliptic, elliptic–ovate, or broadly ovate blades measuring 6.5–18 cm in length and 3.5–7 cm in width. The apex is abruptly acuminate to long-acuminate, while the base ranges from rounded to subcordate, rarely broadly cuneate. The upper surfaces of the leaves are sparsely to densely pubescent with appressed to spreading or erect, curved, or wavy hairs that are 0.3–0.6 mm long, including a tuft of primarily erect hairs at the leaf base. The lower surfaces are moderately pubescent with erect or spreading, curved or nearly straight, white or gray hairs that are 0.4–0.8 mm long, some of which are uncinate and more densely populated along the veins. The blades are thin and grayish to greenish on the lower surface. The margins are entire, and the leaf is palmately 3-veined from the base. Petioles are 1–7 cm long and densely pubescent with straight, erect hairs. Stipules are small and intrapetiolar. The flowers are unisexual and it is dioecious, with flowers appearing in axillary clusters. Staminate (male) flowers feature pedicels 0–2.5 mm long, while pistillate (female) flowers are sessile. The calyx of staminate flowers comprises four boat-shaped, pubescent lobes, each 3–4 mm long with a long–acuminate apex, coherent in bud and separating at anthesis. In contrast, the pistillate calyx is connate into a perigynium, densely pubescent with ascending hairs and a 4-toothed apex. Corolla (petals) are absent in both flower types. Staminate flowers have four staminal filaments folded elastically in the bud and reflexed when pollen is shed. Anthers are reniform and dithecal, opening by longitudinal slits, and the pollen is white. Pistillate flowers have a superior, pseudomonomerous (one fertile carpel and more or less prominent traces of sterile carpel(s)), 1-celled ovary with one basal ovule, a single style, and a stigma approximately 6 mm long, receptive. Staminate flowers feature a vestigial and sterile ovary and a obovoid–urceolate pistillode. The fruit is an achene approximately 2 mm long with a conical apical portion and is not separated from the basal portion by a constriction. Each achene contains one ovoid seed. It is found in diverse mesic forests between 620-1070 meters.