The brutalist movement began in the early 1950s under the architect Le Corbusier, who named his style of crude cement buildings beton brut, which literally meant "raw concrete". This term perfectly encapsulated the vibe the structures exuded, and was soon widespread. When the word was borrowed into English in the 1950s, a slight tweak was made to make it more recognizable as an English term, and, lo, we ended up with the word brutalism. So it's a slightly different word and connotation in our language, but, etymologically, none of that matters, as both brut and English brutal come from Latin brutus (albeit the latter by way of Medieval Latin brutalis, "stupid"), meaning "heavy" or "dull". Yes, this is where the name for Caesar's assassin comes from as well. Curiously enough, brutus does not come from Proto-Italic as most Latin words do. Instead, it came through Oscan from the Proto-Indo-European reconstruction gwere, meaning "heavy".
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd