Perjury

Etymology

From Latin “perjurium” (a false oath), from “perjurare” (to swear falsely), combining “per-” (here meaning “to the detriment of” or “falsely”) with “jurare” (to swear) — the same “jurare” behind “jury” and “justice.” Perjury is, precisely, swearing gone bad.

noun · /PUR-juh-ree/
The crime of deliberately lying under oath in a legal proceeding.
What it names
The reason an oath has teeth — reach for it to name the specific offense that turns a courtroom lie into a prosecutable crime, distinct from ordinary dishonesty.
Example
She faced perjury charges after emails proved her sworn testimony had been a fabrication.
Related idea
Not every courtroom falsehood is perjury: it requires a lie, made under oath, about something material to the case — an honest mistake or a trivial slip doesn’t qualify.