How many letters does the top answer for “sound of something in rapid motion” have?

The most common answer is birr (4 letters).

Crossword clue: sound of something in rapid motion

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

birr 4 letters wn-def

sound of something in rapid motion

whir 4 letters wn-def

sound of something in rapid motion

whirr 5 letters wn-def

sound of something in rapid motion

whirring 8 letters wn-def

sound of something in rapid motion