Under the entry for the word brutum in his dictionary De Verborum Significatu (On the Meaning of Words), the ancient Roman grammarian Sextus Pompeius Festus states: [1, 2, 3]

"Brutum antiqui gravem dicebant."
(The ancients used to say "brutus" for "heavy" or "grave".) [1, 2]

Key Context and Meaning

• Shift in Definition: While the word brutus later came to mean "dull," "stupid," or "irrational" in classical Latin (and eventually evolved into the English word "brute"), Festus preserves the historical Fact that its original, archaic meaning was simply heavy, weighted, or serious. [1, 2, 3]
• Origin of the Surname: This linguistic note is often cited by historians to explain the famous Roman family name (cognomen) Brutus. While popular legend states that Lucius Junius Brutus was given the nickname because he feigned stupidity to avoid being executed by King Tarquin the Proud, Festus’s definition suggests the family name originally meant "The Grave" or "The Serious". [1, 2, 3, 4]

If you want, I can share more details on how other words shifted meaning in early Latin, or explain how Festus’s original text survived through later historical summaries. Which direction would you like to explore? [1, 2]