How many letters does the top answer for “an offspring of a mulatto and a white parent; a person who is one-quarter black” have?

The most common answer is quadroon (8 letters).

Crossword clue: an offspring of a mulatto and a white parent; a person who is one-quarter black

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

quadroon 8 letters wn-def

an offspring of a mulatto and a white parent; a person who is one-quarter black

an offspring of a black and a white parent 50% similar → mulatto