How many letters does the top answer for “a mistake resulting from inattention” have?

The most common answer is lapse (5 letters).

Crossword clue: a mistake resulting from inattention

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

lapse 5 letters wn-def

a mistake resulting from inattention

oversight 9 letters wn-def

a mistake resulting from inattention

a mistake resulting from neglect 50% similar → omission, skip