Actually, it was interesting to read that merriam link, I think they were a bit light on the topic.

I agree, its been around for ever, so its a “word” and we know what someone means when saying it. But it doesn’t make it correct.

IR as in ir-respective it a negation, and it is the same as regard-less, in this case LESS is the negation. So technically ir-regard-less is a double negative, so it equals ‘regards’. Totally technically incorrect and language wise completely illogical ( IL- !! ).

I’ll give you a hint though, Merriam-Webster is an American company, and choses American-isms over the vastly more used British English. Perhaps have a look at the Oxford dictionary for a more lexicographic accurate resource.