Vriddhi (, ) is a Sanskrit word meaning "growth" (from ). In Panini's grammar, it is also a technical term for a group of long vowels. In Indo-European linguistics, it has become a term for the lengthened grade of the ablaut vowel gradation peculiar to the Indo-European languages. A vriddhi-derivation is a word that is derived by such lengthening, a type of formation very common in Sanskrit, but also attested in other languages.