Of the nature of a portent; containing portents; foreshadowing, esp. foreshadowing ill; ominous.
- Of the nature of or constituting a portent; foreboding: "The present aspect of society is portentous of great change” ( Edward Bellamy).
- Full of unspecifiable significance; exciting wonder and awe: "Such a portentous and mysterious monster roused all my curiosity” ( Herman Melville).
- Marked by pompousness; pretentiously weighty.