Brilliant means extremely clever or extremely good. A brilliant scientist, a brilliant idea, that was brilliant.
In British English it is also a general exclamation of approval — Brilliant! — used far more often than the literal sense, and often about very small things. American English uses it mostly for intelligence. The literal, original meaning is shining very brightly: brilliant sunshine, brilliant white. And a brilliant is a diamond cut in a particular way, which is a technical term in jewellery and the source of everything else.
1adjectivebrilliantExtremely clever.
“She is brilliant at explaining things.”
synonyms: gifted, outstanding
2adjectivegoodVery good indeed.
“The whole evening was brilliant.”
3adjectiveshiningShining very brightly.
“A brilliant blue sky and not a cloud in it.”
Too few real examples of this word to estimate which sense is commonest.
brilliant is a degree of quality or brightness.
French brillant comes from Italian brillare, to sparkle, and possibly from Latin beryllus, a beryl — a pale gemstone. So the word for cleverness began as the name of a stone, by way of how it catches the light.
French
brillant
English, today
brilliant
Built from
Borrowed from French brillant. French brillant (late 17th century), present participle of the verb briller, from Italian brillare, possibly from Latin berillus, beryllus (“a beryl, gem, eyeglass”), from Ancient Greek βήρυλλος (“beryl”). by surface analysis, brill(er) + -i- + -ant.
Etymology from Wiktionary, CC BY-SA