1. giving a sign or warning that something momentous or calamitous is likely to happen; ominous
2. pompously self-important; pretentious

Examples

• The dark clouds gathering on the horizon seemed portentous of the storm to come.
• His portentous tone suggested that he had grave news to share.
• The professor’s portentous manner made even simple concepts sound overly dramatic.
• She spoke in a portentous voice about the company’s future.
• The portentous silence in the courtroom made everyone nervous.
• His portentous declarations about art annoyed the other critics.
• The portentous music in the film signaled impending danger.