early 17th century (as homogeneity): from medieval Latin homogeneus, from Greek homogenēs, from homos 'same' + genos 'race, kind'
The usual spelling is homogeneous, and the spelling homogenous is traditionally regarded as an error. Homogenous is a different word, a specialized biological term meaning ‘having a common descent’, which has been largely replaced by homologous. From the evidence of the Oxford English Corpus, the spelling homogeneous has become significantly less common since 2000, and around a third of citations for the word now use the form homogenous. This can now be regarded as an established variant.