In early medieval Irish texts, you come across the concepts as dessel (deisil, deaseal) and túaithbiul, for instance in Togail Bruidne Da Derga paragraph 16, when Conare is given the geasa or taboos that will govern his kingship. He is told:
Ní thuidchis deaseal Teamra & túaithbiul m-Breg.
You are not to go righthandwise round Tara and lefthandwise around Brega. (Translation taken from Jeffrey Gantz, Early Irish Myths and Sagas (Penguin, 1981), p. 66)
If you look at the Dictionary of the Irish language online, under dessel it gives the following definitions: a. (as noun) direction of the sun, right-hand course, righthand-wise; b. (as adj.) from the idea that sunwise was a lucky or auspicious direction comes the extended of more generalized meaning what is lucky, favourable, propitious. (See here for more detail.) It comes originally from dess, "right" (=/= left), cognate with Latin dexter.
And the opposite, tuaithbel: a. a turning lefthandwise, against the sun, withershins; b. lefthandwise, from left to right, withershins. (See here for more detail.) I'm not entirely clear on the etymology of this, but túaisre is a related adverb meaning "on the left", so it seems to be linking directly to the concept of "left".