How many letters does the top answer for “a narrowing that reduces the flow through a channel” have?

The most common answer is bottleneck (10 letters).

Crossword clue: a narrowing that reduces the flow through a channel

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

bottleneck 10 letters wn-def

a narrowing that reduces the flow through a channel

constriction 12 letters wn-def

a narrowing that reduces the flow through a channel