Origins
Brilliant may have crossed more language families than almost any word in English.βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ The leading theory traces it from French brillant ('shining') to Italian brillare ('to sparkle') to Latin beryllus ('beryl gemstone') to Greek bαΈryllos, to Prakrit veαΈ·uriya, to a Dravidian root meaning 'to be white' or 'to shine'. From southern India to every English dictionary.
The beryl connection is debated but influential. Beryl is a pale green mineral that, when cut, produces the gemstone emerald. Its sparkle may have given Italian the verb brillare in the 16th century, though some scholars prefer a simpler onomatopoeic origin.
Figurative Development
English borrowed brilliant from French in the 1680s, initially for physical light. The intellectual sense β a brilliant scholar, a brilliant idea β appeared by the mid-18th century. The metaphor of intelligence as light runs deep in European languages: illumination, enlightenment, bright student, dim-witted.
In British English, brilliant acquired a colloquial sense of general approval ('That's brilliant!') by the 20th century. The word that possibly began as a description of South Indian gemstone lustre now serves as casual praise in Bristol pubs.