Where does “echtrad” come from?

echtrad (Middle Irish) comes from Old Irish echtra, from Old Irish echtar, from Proto-Celtic *exteros, from Proto-Indo-European h₁eǵʰs — out.

Ancestry of “echtrad”, step by step

Step	Language	Word	Meaning
1	Old Irish	echtra	—
2	Old Irish	echtar	without, outside
3	Proto-Celtic	*exteros	—
4	Proto-Indo-European	h₁eǵʰs	out

echtrad — Etymology, Origin & Word History | Etymology Explorer