Meaning

adjective not pertinent to the matter under consideration

adjective statistically unrelated

adjective having a set of mutually perpendicular axes; meeting at right angles

originFrom Middle French orthogonal, in turn from Medieval Latin orthogōnālis and Latin orthogōnius (“right-angled”), ultimately from Ancient Greek ὀρθογώνιος (orthogṓnios, “rectangular”). By surface analysis, ortho- + -gon + -al.

Etymology from Wiktionary, CC BY-SA 3.0