Definitions

1. adjective

giving a sign of what is to come; ominous

“The portentous clouds gathered in the sky before the storm hit.”

2. noun

an event or sign that is thought to foretell the future

“The king’s illness was seen as a portentous sign of his impending death.”

3. verb

to give signs or omens of what is to come

“The prophecy portended great change for the kingdom.”