Wurdahuzdą: Proto-Germanic dictionary

noun feminine ōn-stem forms feminine agent nouns and female personal nouns corresponding to masculine *-(i)jô (forms masculine agent nouns) From Early Germanic *-(i)jōn-, the feminine weak n-stem counterpart of masculine *-(i)jô. Ultimately connected with the Proto-Indo-European individualizing n-stem suffix, which formed personal nouns and, from verbal roots, agent nouns meaning ‘the one who does X’ Pronk 2015: 327–29. The feminine shape reflects the Proto-Germanic amalgamation of inherited feminine eh₂-stems with n-stem inflection: old h₂-stems were transferred to the feminine ōn-stems after their nominatives became formally indistinguishable, and a similar process produced the PGmc īn-stems from PIE ih₂-stems Kroonen 2011a: 64–65 Lehmann 1986a: §4.2.2. Desclension

The suffix varies as *-jǭ/*-ijǭ based on Siever’s Law: the basic *-jǭ form is used after a “light” syllable (a short vowel followed by a single consonant), and otherwise, the form becomes *-ijǭ.