Of the nature of a portent; containing portents; foreshadowing, esp. foreshadowing ill; ominous.

Hence: Monstrous; prodigious; wonderful; dreadful; as, a beast of portentous size.

of momentous or ominous significance; "such a portentous...monster raised all my curiosity"- Herman Melville; "a prodigious vision"

puffed up with vanity; "a grandiloquent and boastful manner"; "overblown oratory"; "a pompous speech"; "pseudo-scientific gobbledygook and pontifical hooey"- Newsweek