acceleration
n//ækˌsɛl.əˈɹeɪ.ʃən//acceleration
(uncountable) The act of accelerating, or the state of being accelerated; increase of motion or action; as opposed to retardation or deceleration.
(countable) The amount by which a speed or velocity increases (and so a scalar quantity or a vector quantity).
(physics) The change of velocity with respect to time (can include deceleration or changing direction).