Plain English Meaning
To slow down. The aircraft is going more slowly than it was a moment ago.
Full Definition
To reduce speed; in aviation, the act of slowing the aircraft's velocity, whether in flight or on the ground, through reduced thrust, increased drag, braking, or a combination of these.
Context Anchor
Seen in thrust and air resistance discussions, airspeed control, landing, and stopping after touchdown.
Derivation
From Latin de- (down, away from) and celer (swift, fast). Literally 'to take away swiftness.' The opposite of accelerate.
Why Pilots Care
Proper deceleration prevents excessive on and ensures safe speed management throughout .