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

The most common answer is buck (4 letters).

Crossword clue: author of 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

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

wrote east wind: west wind 60% similar → buck

a wind from the east 50% similar → easterly