How many letters does the top answer for “once in six years.” have?

The most common answer is sexennially (11 letters).

Crossword clue: once in six years.

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

sexennially 11 letters web-def

Once in six years.

once in a hundred years. 50% similar → centennially

once in four years. 50% similar → quadrennially

once in seven years. 50% similar → septennially

once in three years. 50% similar → triennially

once in two years. 50% similar → biennially