Yaska (5th century BCE?) is traditionally credited with writing the Nirukta, a Vedic treatise that provides etymological explanations for ancient terms.
Nearly a fourth of the Vedic terms occur just once.
As the spoken language evolved, the meanings of many of these
terms had become either ambiguous or altogether forgotten by Yaska's time.
Although it is evident that Yaska is guessing at times—for
example, when contemporary linguists may draw parallels with the Iranian
Avesta, a comparable religious text—his work proved invaluable to subsequent
readers.
You may also want to read more about Hinduism here.
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