Where does “in éineacht” come from?

in éineacht (Irish) comes from Irish éineacht, from Old Irish oínḟecht, from Old Irish óen, from Proto-Celtic oinos, from Proto-Indo-European óynos — one; single.

in éineacht (Irish): at the same time, at once

Definitions

at the same time, at once

Ancestry of “in éineacht”, step by step

in éineacht traces back through two separate lines of ancestry.

via Irish éineacht

Step	Language	Word	Meaning
1	Irish	éineacht	once, one time
2	Old Irish	oínḟecht	—
3	Old Irish	óen	one
4	Proto-Celtic	oinos	one
5	Proto-Indo-European	óynos	one; single

via Irish i

Step	Language	Word	Meaning
1	Irish	i	in
2	Old Irish	i	in; into; For quotations using this term, see...
3	Proto-Celtic	eni	—
4	Proto-Indo-European	én	in

Every word from Proto-Indo-European óynos →Every word from Proto-Celtic oinos →Every word from Old Irish óen →