Illegitimi Non Carborundum

Illegitimi non carborundum is a mock-Latin aphorism meaning "Don't let the bastards grind you down". Carborundum, also known as silicon carbide, is an industrial abrasive material, but its name resembles a Latin gerundive.

The phrase originated during World War II and is attributed to British army intelligence. It was a motto of US Army general "Vinegar" Joe Stillwell and was further popularized in the US by 1964 presidential candidate Barry Goldwater. It is also the first line of the Harvard fight song Ten Thousand Men of Harvard.

There are a number of versions for the phrase referenced in popular culture.