How many letters does the top answer for “the act of accelerating; increasing the speed” have?

The most common answer is acceleration (12 letters).

Crossword clue: the act of accelerating; increasing the speed

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

acceleration 12 letters wn-def

the act of accelerating; increasing the speed

speedup 7 letters wn-def

the act of accelerating; increasing the speed