Coprosma waimeae is a shrub that grows between 1.5 and 4 meters tall. The branches are lax, with the youngest being glabrous to sparsely pilose. The leaves are simple and opposite. The blades are narrowly elliptic–ovate to oblong–elliptic or elliptic–obovate, measuring 58–115 mm long and 23–45 mm wide. The leaf apex is obtuse or rounded, often mucronulate, and the base is broad to narrowly cuneate. Leaf surfaces are glabrous or sparsely appressed pilose along the midrib or occasionally on lateral veins, and the blades are thin and coriaceous. The leaf margins are entire, and the venation is pinnate. Petioles range from 4 to 15 mm long. The stipules are deltate, 2–3 mm long, connate for half to three-quarters of their length, sometimes splitting down one or both sides, glabrous with sometimes sparsely ciliate margins or base, and have a short–acuminate apex with an appendage. The flowers occur in clusters of 1–4(–8), are 8–9-merous, and are borne on peduncles 6–20 mm long, which are puberulent or glabrous. The flowers are unisexual and dioecious, often heterostylous, and insect-pollinated. The calyx of staminate flowers is cup-shaped and 2–2.5 mm long, while the pistillate flowers have a 1.2–1.5 mm long calyx. The corolla of staminate flowers is funnelform, 8–10 mm long, with lobes about 4–5 mm long; the corolla of pistillate flowers is narrowly funnelform, 3.1–4 mm long, with lobes 2.2–2.7 mm long, and usually has a nectary disk. Stamens number 4-5(-10), are alternate with the corolla lobes and are inserted at the base of the corolla tube; filaments are long-exserted with pendulous anthers that are dithecal and open by longitudinal slits. The ovary is inferior, occasionally partly so, rarely superior, and 2(-4)-celled; there is one ovule per cell, which is basal and anatropous. The style has as many lobes as carpels, 2(-4)-lobed, divided nearly to the base, terminal and slender; stigmas are lobed or capitate, long-exserted, papillose-hirsute, and either dry or occasionally wet. The fruit is drupaceous, juicy, bright orange, and subglobose, measuring 8.5–11 mm long, with an apex with persistent calyx teeth. Each fruit contains 2(-4) 1-seeded planoconvex pyrenes. The seeds have well-developed oily endosperm, though endosperm can occasionally be scanty or absent. It is found in mesic forests at 580-1,070 meters.