12 letters · 23 points in Scrabble
adjective insanely irresponsible
originFrom crack + brained. The word is centuries old, and the original imagery is of a brain that is cracked (broken), but the advent of crack cocaine produced a new surface analysis whereby the word now also suggests a crack(rock)-addled brain. But even with that difference in referents, cognation is involved regardless.
Etymology from Wiktionary, CC BY-SA 3.0