The word "atom" comes from the Greek (ἀτόμος) "atomos", "indivisible", from (ἀ)-, "not," and τόμος, "a cut." The first historical mention of the word atom came from works by the Greek philosopher Democritus, around 400 BC. Atomic theory stayed as a mostly philosophical subject, with not much actual scientific investigation or study, until the development of chemistry in the 1650s.