How many letters does the top answer for “a channel for the water current that turns a millwheel” have?

The most common answer is millrace (8 letters).

Crossword clue: a channel for the water current that turns a millwheel

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

millrace 8 letters wn-def

a channel for the water current that turns a millwheel

millrun 7 letters wn-def

a channel for the water current that turns a millwheel