ถ้อยคำจูจูjuju

The word reached English print through colonial officials. James George Frazer published it in Folk-Lore volume XXVI under the title 'A Priest-King in Nigeria', from a communication he received from P. A. Talbot, District Commissioner in southern Nigeria. Talbot described the dominant Ju-Ju of Elele, a town in the north-west of the Degema district, as a Priest-King elected for a term of seven years, and wrote: 'The whole prosperity of the town, especially the fruitfulness of farm, byre, and marriage-bed, was linked with his life. Should he fall sick, therefore, it entailed famine and grave disaster upon the inhabitants ...'

Others were already writing it down. Le Comte C. N. de Cardi documented the practice among Igbo, Ibibio and Yoruba people of the Niger Delta in an article of 1899; Alan Maxwell Boisragon in a book of 1897.

On what the word covers, Wikipedia's article is careful and worth quoting rather than paraphrasing: according to some authors, 'It is neither good nor bad, but it may be used for constructive purposes as well as for nefarious deeds.' Its commonest reported use is the treatment of physical and spiritual complaints — insect and animal bites, and the countering of curses. It is also used to bind a contract or secure compliance, with the practitioner paid for the service. Used against somebody, it is reported as a means of revenge and of causing misfortune.

Inference — the etymological fight matters because of what each answer implies. Hausa 'evil spirit' makes the word a local name for a serious thing. French joujou makes it a European joke about somebody else's religion. Which root a nineteenth-century writer preferred has usually said more about the writer than about the word, and the sources have not settled it.