Eleutherodactylus adelus is a tiny frog, with males reaching only 12 mm and females up to 15 mm in SVL. The skin of the dorsum is tuberculate and has a pair of paravertebral folds at mid-dorsum. The venter is partially areolate, becoming gradually smooth toward chest. The digital discs are very small. There is no webbing between the toes. Vomerine teeth are present, behind the choanae, in a short and arched series (Diaz et al. 2003).

This species has a wide longitudinal dark-bordered brown zone on the dorsum, which becomes narrow and pointed toward the snout and is outlined by narrow light stripes. There is a suprainguinal black stripe bordering the light margins of the dorsal zone in the posterior half of the body. Two shallow suprascapular tubercles are present and are frequently light-colored. The flanks are a contrasting light grayish tan, sometimes with a slight green or reddish wash. The supratympanic fold is conspicuously emphasized in black and followed on the flanks by a large black diagonal stripe. Limbs have moderate to faint brown cross bars; the forearms are reddish brown. The belly is greenish or flesh-colored. Sometimes individuals have scattered dots on the throat and belly and the ventral surface of the thighs (Diaz et al. 2003).
 
This species is a member of the subgenus Euhyas (Heinicke et al. 2007).

Etymology- The name derives from the Greek word adelos, meaning concealed, in allusion to the secretive habits of this frog, which immediately stops calling when approached (Diaz et al. 2003).