How many letters does the top answer for “the first month of the year, containing thirty-one days.” have?

The most common answer is january (7 letters).

Crossword clue: the first month of the year, containing thirty-one days.

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

january 7 letters web-def

the first month of the year; begins 10 days after the winter solstice