Where does “is” come from?

is (Irish) comes from Old Irish ís, from Proto-Celtic ɸīssu, from Proto-Indo-European pedsú, from Proto-Indo-European pṓds, from Proto-Indo-European póds, from Proto-Indo-European ped- — to walk, to step; to stumble, to fall.

is (Irish): reduced form of agus; Present/future realis...