How many letters does the top answer for “a deep gorge, ravine, or gulch, between high and steep banks, worn by water courses.” have?

The most common answer is canon (5 letters).

Crossword clue: a deep gorge, ravine, or gulch, between high and steep banks, worn by water courses.

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

canon 5 letters web-def

a rule or especially body of rules or principles generally established as valid and fundamental in a field of art or phi

canyon 6 letters web-def

a ravine formed by a river in an area with little rainfall