How many letters does the top answer for “commit a faux pas or a fault or make a serious mistake” have?

The most common answer is blunder (7 letters).

Crossword clue: commit a faux pas or a fault or make a serious mistake

3 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

blunder 7 letters wn-def

an embarrassing mistake

boob 4 letters wn-def

either of two soft fleshy milk-secreting glandular organs on the chest of a woman

goof 4 letters wn-def

commit a faux pas or a fault or make a serious mistake