PORTENT'OUS, adjective [Latin portentosus.] Ominous; foreshowing ill. Ignorance and superstition hold meteors to be portentous 1. Monstrous; prodigious; wonderful; in an ill sense. No beast of more portentous size, In the Hercynian forest lies.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI