Por‐tent″ous (?), a. [L. portentosus.] 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. Roscommon.
— Por‐tent″ous‐ly, adv. — Por‐tent″ous‐ness, n.