Entry 2 senses Webster, 1913 Portentous /pôr-tĕn'-təs/ · Por·tent·ous · IPA /pɔrˈtɛn(t)əs/ 01 a. Of the nature of a portent; containing portents; foreshadowing, esp. foreshadowing ill; ominous. 1. Of the nature of a portent; containing portents; foreshadowing, esp. foreshadowing ill; ominous. “For, I believe, they are portentous things.” — Shak. “Victories of strange and almost portentous splendor.” — Macaulay. 2. Hence: Monstrous; prodigious; wonderful; dreadful; as, a beast of portentous size.