12 letters · 14 points in Scrabble
adverb regardless; a combination of irrespective and regardless sometimes used humorously
originProbably a blend of irrespective + regardless; the word can also be analysed as ir- + regardless because it is possible that the prefix ir- was added to amplify the negative in regardless just as plain negatives often did at the time the word came into use (and still do in dialects).
Etymology from Wiktionary, CC BY-SA 3.0