How many letters does the top answer for “a combining form meaning eight; as in octodecimal, octodecimal, octolocular.” have?

The most common answer is octa (4 letters).

Crossword clue: a combining form meaning eight; as in octodecimal, octodecimal, octolocular.

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

octa 4 letters web-def

A prefix meaning eight. See Octo-.

octo 4 letters web-def

A combining form meaning eight; as in octodecimal, octodecimal, octolocular.