The story
- Proto-Indo-European*(h₁)ém-no-
- Proto-Germanic*ebnaz
- Proto-Germanic*ebnassuz
- Proto-West Germanic*ebnassī
- Old Englishefennes
- Middle Englishevennesse
- English todayevenness
Inherited from Middle English evennesse, from Old English efennes, from Proto-West Germanic *ebnassī, from Proto-Germanic *ebnassuz, from *ebnaz (“even”) + *-assuz (“-ness”). By surface analysis, even (“flat”) + -ness.
Etymology from Wiktionary, CC BY-SA 4.0.