a. [ L. portentosus. ] 1. Of the nature of a portent; containing portents; foreshadowing, esp. foreshadowing ill; ominous. [ 1913 Webster ]
For, I believe, they are portentous things. Shak. [ 1913 Webster ]
Victories of strange and almost portentous splendor. Macaulay. [ 1913 Webster ]
2. Hence: Monstrous; prodigious; wonderful; dreadful; as, a beast of portentous size. Roscommon. [ 1913 Webster ]
-- Por*tent"ous*ly, adv. -- Por*tent"ous*ness, n. [ 1913 Webster ]