How many letters does the top answer for “a movement in opposition to another.” have?

The most common answer is countermove (11 letters).

Crossword clue: a movement in opposition to another.

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

countermove 11 letters web-def

an attack by a defending force against an attacking enemy force in order to regain lost ground or cut off enemy advance

countermovement 15 letters web-def

A movement in opposition to another.

another word for movement 67% similar → motility