Where does “rèitire” come from?

rèitire (Scottish Gaelic) comes from Scottish Gaelic rèitich, from Scottish Gaelic rèite, from Old Irish réidid, from Proto-Celtic rēdeti, from Proto-Indo-European Hreydʰ- — to ride, move.

Ancestry of “rèitire”, step by step

Step	Language	Word	Meaning
1	Scottish Gaelic	rèitich	accommodate, adjust, agree, arrange, assort,...
2	Scottish Gaelic	rèite	accommodation, agreement, adjustment,...
3	Old Irish	réidid	to ride, drive
4	Proto-Celtic	rēdeti	to ride, move
5	Proto-Indo-European	Hreydʰ-	to ride, move

Every word from Proto-Indo-European Hreydʰ- →Every word from Proto-Celtic rēdeti →Every word from Old Irish réidid →