Etmopterus dislineatus is an extremely slender species with a relatively short head and very elongate caudal peduncle. The eyes are rather narrow, and the upper eyelid has a pale naked patch. Denticles are extremely dense, bristle-like, and not arranged in defined rows. The first dorsal fin is small and rounded, half the size of the second.
Coloration is light silvery-brown above, becoming darker below with fine dark horizontal lines forming a series of fine dots and dashes on the upper half of body. There are distinct black markings near the pelvic fins and on the caudal peduncle, mid caudal fin, and upper fin tip. Reproduction is ovoviviparous.