Etymology 1 
From Middle English ey, from Old English ǣġ ("egg"; ǣġru in the plural), from Proto-Germanic *ajją, *ajjaz (“egg”), from Proto-Indo-European *ōuyo-, *h₂ōwyóm (“egg”). Cognate with West Frisian aai (“egg”), Dutch ei (“egg”), German Low German Ei (“egg”), German Ei (“egg”), Danish æg (“egg”), Swedish ägg (“egg”), Icelandic egg (“egg”), Scottish Gaelic ugh (“egg”), Latin ōvum (“egg”). Was replaced by egg in the 16th century.
ey (plural eyren) (obsolete since the sixteenth century)
Etymology 2 
Coined by Christine M. Elverson by removing the "th" from they.
- (neologism) they (singular). Gender-neutral third-person singular subject pronoun, coordinate with gendered pronouns he and she.
- 1975 August 23, Black, Judie, “Ey has a word for it”, Chicago Tribune, page 12:
- 1996 December 22, Worth, Shirley, “New To Yoga”, alt.yoga, Usenet:
- I'm not familiar with this book, but I encourage Marksmill to look for it-- and while ey is at it, to also look at a number of other books.
- 1997 November 25, Dawson, Scott Robert, “Who Pays for Cellular Calls”, alt.cellular, Usenet:
- For more examples of usage of this term, see the citations page.
Coordinate terms 
See also 
The dative singular eyju / eyjunnar also occurs, but is on its own indistinguishable from the dative of the weak form eyja.
Old Norse 
From Proto-Germanic *awjō.