How many letters does the top answer for “classical antiquity scientist” have?

The most common answer is gibbon (6 letters).

Crossword clue: classical antiquity scientist

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

gibbon 6 letters wd-fact-v3

smallest and most perfectly anthropoid arboreal ape having long arms and no tail; of southern Asia and East Indies

mommsen 7 letters wd-fact-v3

German historian noted for his history of Rome (1817-1903)

classical music scientist 50% similar → einstein

classical mythology scientist 50% similar → hamilton

classical philology scientist 50% similar → diels, gelzer, mommsen

late antiquity scientist 50% similar → dahn