'phratry' originates from Greek, specifically the word 'phratria', where the root 'phrā́tēr' meant 'member of a clan, brother'.

'phratry' passed into English via Latin or New Latin from Greek 'phratria' and was recorded in English from the early 17th century as the borrowing stabilized into the modern form 'phratry'.

Initially it meant 'a brotherhood or group of kinsmen'; over time it came to be used more technically in anthropology and classical studies to mean 'a clan-like subdivision (of a tribe) in ancient Greek society', a usage that persists today.