Delissea waianaeensis is a shrub that grows 1–2.5 meters tall. The stem is usually branched, erect, or ascending, with a light gray or brown color, unarmed, 6–14 mm in diameter, smooth (glabrous), and moderately leafy toward the apex, featuring numerous helically arranged leaf scars. The plant’s latex is white and viscous. The leaves are simple and alternate, scattered along the distal portion of the stem. The blades are ovate or narrowly ovate, measuring 11–24 cm long and 4.5–15 cm wide, with an acute, acuminate, or cuspidate apex and a truncate, subcordate, rounded, or obtuse base. The leaf surfaces are smooth (glabrous), and the blades are fleshy when fresh and turn membranous to somewhat chartaceous when dry. The margins are commonly coarsely biserrate, often with 1–4 triangular lobules per side toward the base. The leaves are pinnately veined and have cylindrical (terete) petioles that are 7.0–19.5 cm long, about half as long as slightly longer than the lamina. It has several axillary, racemose, and anauxotelic inflorescences per stem, each with 5–12 flowers. The peduncle and rachis are ascending or spreading and glabrous, with the peduncle measuring 8–25 mm long and the rachis 4–34 mm long. The bracts are triangular or deltate and persistent, subtending pedicels 9–15 mm long, ascending or spreading. The flowers are tetracyclic, bisexual (perfect), complete, protandrous, epigynous (having the ovary enclosed in the receptacle, with the stamens and other floral parts situated above), and resupinate. The calyx is synsepalous and actinomorphic (radially symmetric), with a glabrous tube adnate to the ovary. The corolla is white, sympetalous, zygomorphic (bilaterally symmetric), bilabiate, and glabrous, measuring 45–62 mm long. It has five syngenesious (arrangement of stamens where their anthers are fused while their filaments are free) stamens that are antisepalous and exserted. The filament tube measures 35–51 mm long, and the anther tube is glabrous or sparsely pubescent. The ovary is inferior, 2-loculed, with many ovules and an axile placentation. The fruit is a small purple, fleshy, thin-walled berry that is globose, cylindrical, or ellipsoid, measuring 7–16 mm long and 7–11 mm in diameter. The seeds are numerous, grayish-white, and transversely rugose. It is found in wet to mesic forests at elevations of 245–760 meters.