The word keeps its hand-making image even in a factory full of machines.
Latin manus means hand. The phrase manu factus meant made by hand and lies behind Medieval Latin manufactura and French manufacture. Modern manufacture can use machinery as well as hands.
French and Medieval Latin are explained but omitted from the slots; no claim is made that early English excluded machinery.
Sources
- Merriam-Webster: manual
Latin manus is the hand noun also behind manualis.
- Merriam-Webster: manufacture
The entry gives the French and Medieval Latin route from manu factus, literally made by hand; the modern definition includes machinery.