How many letters does the top answer for “author of the swiss family robinson” have?

The most common answer is wyss (4 letters).

Crossword clue: author of the swiss family robinson

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

wyss 4 letters wd-fact-v3

a state in the western United States; mountainous in the west and north with the Great Plains in the east

wrote the swiss family robinson 60% similar → wyss