irregardless
The word is regardless. The extra syllable is doing damage, not work.
-
Wrong: Irregardless of the cost, we’re doing it.
Right: Regardless of the cost, we’re doing it.
-less already means without. Ir- means not. Together they cancel.
Why it’s wrong
Regardless = regard + -less = without regard. The suffix already does the negating.
Bolting ir- on the front adds a second negative, so the word technically means not without regard—the opposite of what anyone using it intends. It’s a double negative wearing a suit.
The annoying part
It’s in the dictionary. Merriam-Webster lists it, marked nonstandard, because it’s been recorded since the early 1900s and dictionaries record what people say.
Being in the dictionary is not the same as being usable in professional writing. Nonstandard is a warning label. Regardless is one syllable shorter and nobody has ever objected to it.
Now go drop two syllables.