Trunk (5-)10-20 m tall, erect, 15-25 cm dbh, columnar, usually naked, sometimes, particularly in closed forest, upper portion partially or completely enclosed in a mat of persistent leafsheath fibers; trunks of juveniles less than ca. 6-8 m tall usually completely enclosed in this mat; mat, when present, usually 20-30 cm thick. Leaves IS-ca. 30; petiole (1-)1.5-2.5(-3) m long, 2.3-3.4 cm wide at attachment to blade; sheath tomentose, the trichomes of two intermixed types: 1) soft, stellate trichomes, ca. 0.5 mm long, basally ferruginous, with free, white distal ends and 2) coarser, longer, wavy, twisted, compressed trichomes, these larger trichomes sparsest, shortest (ca. 1.5 mm long), and lightest in color (± tannish) on the basal portion of the sheath, becoming progressively denser, longer (to 9 mm long), and darker (rufous) distally; sheath disintegrating and fraying into fine, loosely woven, pendulous, filiform, typically ± terete fibers, 0.3-0.5 mm diam.; hastula appressed to or slightly elevated above the blade, 2.3-3.4 x 2.4-3.9 cm, 0.7-1.4 times as wide as long, broadly to very broadly triangular, usually cuspidate apically; costa 16.5-38.5 cm long; blade 131-170 cm long centrally, 62-136 cm long laterally, divided into single-fold segments, except for lateral-most segment of each blade half, composed of 2(-4) folds; central division extending to within 46-67 cm of (1/2-2/3 to) base, the lateral-most division extending to within 11.5-19.0 cm of (ca. 4/5 to) base; folds per blade half 25-35; widest single-fold segment 4.3-5.0 cm wide. Inflorescences with flowers or fruit to ca. 5(-8), plus ca. 5(-7) marcescent; primary-axis 1.2-2.1 m long; inflorescence bracts Ianate, with trichomes 2-8 mm long; peduncle 0.2-0.8 m long; prophyll ca. 25 x 8.0-10.0 cm; peduncular bracts 6-7,27.0-45.0 cm long; rachis 0.9-1.4 m long; rachis bracts 14.0-47.0 cm long; first-order branches 9-12; axes creamy yellow, their primary-axes 12.0-58.5 cm long, with unbranched proximal portion 2.5-37.0 cm long, the branched distal portion 6.0-32.0 cm long; prophyll 10.5-40.5 cm long; rachillae typically 40-50 per basal first-order branch, 10-20 per apical first-order branch, 3.0-15.5 cm long, tomentose, the trichomes (tannish to) ferruginous, 0.2-0.3 mm long; flower-bearing spurs 0.2-0.8(-1.2) mm long, the subtending bracteole 0.7-2.0 mm long, 0.4-1.0 mm wide basally. Floral receptacle 0.7-1.7 mm long; calyx 3.5-5.4 mm long, free distally from corolla for 1/2-2/3 its length, creamy yellow, the lobes 0.5-0.8 mm long; corolla 4.0-6.0 mm long, connate basally for 1/5-1/3 its length, mostly creamy yellow, the lobes valvate, with parallel sides and mucronulate apices, fleshy, adaxially furrowed with involute or thickened margins, forming a hood apically, persistent; filaments 2.1-4.0 mm long, connate basally for 1.1-2.0 mm (2/5-3/5 their length), cream-colored, stamen-cup shorter than or ± same length as calyx-cup, 1.5-2.2 mm diam., anthers 2.3-3.5 x 0.9-1.3 mm; pollen 25-30 x 20-30 pm, tectum on non-apertural face coarsely perforate to reticulate; gynoecium 2.5-3.4 x 1.1-1.6 mm, carpels 1.1-1.6 x 0.7-1.3 mm, cream-colored, styles 1.5-2.2 mm long, cream-colored. Fruit 1.6-2.1 cm diam. Seed 1.0-1.2 x 1.3-1.5 cm.
Colpothrinax cookii is restricted to the upper slopes and crests of ridges of premontane wet forests above 700 m elevation and, like C. aphanopetala, often occurs in association with Euterpe precatoria Mart. Both staminate and pistillate anthesis in the strong-smelling, creamy yellow flowers of C. cookii appear to occur while the reproductive parts are still enclosed within the unopened corollas, suggesting beetle pollination (Henderson 1986).
The leaves of C. cookii are sometimes used for thatching and for making brooms. Local people in Honduras and Belize (Gerrit Davidse, pers. comm.) have admitted to setting fire to the mat of highly flammable leaf-sheath fibers enclosing the trunks of some individuals merely for the pyrotechnic display.