1. in a way that suggests something important or ominous will happen
2. in a pompous or self-important manner

Examples

• The storm clouds gathered portentously on the horizon.
• He spoke portentously about the company’s future.
• The old woman nodded portentously at the news.
• The professor portentously announced his groundbreaking theory.
• Thunder rumbled portentously in the distance.
• She portentously declared that change was coming.
• The politician portentously warned of economic disaster.