O.E. agen "one's own," lit. "possessed by," from P.Gmc. *aigana- "possessed, owned" (cf. O.S. egan, O.Fris. egin, O.N. eiginn, Du. eigen, Ger. eigen "own"), from pp. of PIE *aik- "to be master of, possess," source of O.E. agan "to have" (see owe).
evolved in early M.E. from O.E. geagnian, from root agan "to have, to own" (see own), and in part from own (adj.) (q.v.). It became obsolete after c.1300, but was revived early 17c., in part as a back-formation of owner (mid-14c.), which continued. To own up "make full confession" is from 1853.