Portend is a verb. It means (1) to serve as an omen or a warning of, or (2) to forecast. Portent is a noun. It has two main definitions: (1) an indication of something calamitous about to occur, and (2) a prophetic or threatening quality. The two words are closely related—both derived from the Latin portendere, meaning to indicate—but they have different functions and share no common ground in today’s English.
Their corresponding adjective is portentous, which does not have an i.
The worst portent for health-care reform last night wasn’t the repeal vote itself, but what didn’t come with it. [Washington Post]
The woman photographed before a metallic expanse of ocean is a personification of grim portent. [Guardian]
I took this vignette as a worrying portent of this revolution’s future. [The National]
Since 2000, the Hispanic population has grown by 497,316 to 2.03 million, a trend that could portend shifts in political clout. [USA Today]
They leave oceans of public debt that portend higher taxes and real interest rates, in addition to inflationary threats.
[Mail & Guardian Online]
The uprisings sweeping across the Middle East portend a political transformation as significant as those of 1989. [Open Democracy]