shampoo: [18] Hindi chāmpō means ‘press!’ It is an imperative form of chāmpnā ‘press’, or more specifically ‘knead the muscles’. The English in India took the word up in the 18th century as a verb meaning ‘massage’, but by the middle of the 19th century we find it being used in the accepted modern sense, ‘wash the hair’. The linking factor was presumably the vigorous massaging action typically applied to the scalp when shampooing the hair.
shampoo (v.)
1762, "to massage," from Anglo-Indian shampoo, from Hindi champo, imperative of champna "to press, knead the muscles," perhaps from Sanskrit capayati "pounds, kneads." Meaning "wash the hair" first recorded 1860; extended 1954 to carpets, upholstery, etc. Related: Shampooed; shampooing.