How many letters does the top answer for “director of modern dance” have?

The most common answer is fuller (6 letters).

Crossword clue: director of modern dance

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

fuller 6 letters wd-fact-v3

a workman who fulls (cleans and thickens) freshly woven cloth for a living

director of lord of the dance 50% similar → flatley