ceiling B1

/ˈsilɪŋ/ The inside surface at the top of a room.

cellar B2

/ˈsɛləɹ/ An underground room beneath a building, used for storage.

celerity C2+

/səˈlɛrəti/ swiftness of movement or action; speed

decelerate C2+

/diˈsɛləˌreɪt/ to reduce speed; to slow down

acceleration C2+

/ækˌsɛləˈreɪʃən/ the rate of increase of speed or, more generally, the act of speeding up

accelerator C2+

/əkˈsɛləreɪtɚ/ a device or thing that increases speed, especially a car's gas pedal