When someone is completely wrong about a statement but they are either too dumb or stubborn to admit they are wrong. Most of the time it is a combination of both. Once confronted with clear evidence they were completely wrong they will state they knew the answer but stated the wrong answer for effect.

n. The birth name of somebody who has changed their name. Most commonly attributed to trans people, but can be attributed to any person who has changed their name. (sometimes written as two words: dead name)

v. 1. To call somebody by their deadname.
v. 2. To out somebody's deadname to the public.