How many letters does the top answer for “wrote east wind: west wind” have?

The most common answer is buck (4 letters).

Crossword clue: wrote east wind: west wind

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

buck 4 letters wd-fact-v3

to strive with determination

author of east wind: west wind 60% similar → buck

wind that blows from west to east 60% similar → wester

a wind from the east 50% similar → easterly