In Hindi, "shampoo" comes from the word "champo", which means "to massage".
This is because in ancient India, people used to massage their hair with oils and herbs, a practice that is still common today. The word "champo" evolved into "shampoo" as it was adopted by the English language.
So, while we use "shampoo" to refer to the product itself, it originally meant the action of massaging the hair.