Overweening

1 : arrogant, presumptuous
*2 : immoderate, exaggerated

Example sentence:
The overweening ambition of the novel's principal character eventually leads to his downfall.

Did you know?
"The overweening conceit which the greater part of men have of their own abilities is an ancient evil remarked by the philosophers and moralists of all ages." So wrote Adam Smith in his The Wealth of Nations. But while overweening conceit might be an age-old evil, the word "overweening" has only been part of English since the 14th century. It developed from the Middle English "overwening," the present participle of the verb "overwenen," which meant "to be arrogant." That term derived in turn from "wenen," which meant "to think" or "to imagine." Today, the adjective "overweening" is the most widely used of the "wenen" descendants, but historical texts also occasionally include "overween," a term for thinking too highly of your own opinion.