Mid 19th century; earliest use found in William S. Hamilton (1788–1856), philosopher. From post-classical Latin diallelon from ancient Greek δι' ἀλλήλων through or by means of one another (in δι' ἀλλήλων δεῖξις reciprocal proof (Aristotle)) from διά through + ἀλλήλων one another, reduplicated formation from ἄλλος other.