Acknowledge - to say that you have heard and understood. It is important that the controller listens carefully to the nature of the emergency, requests clarification if in doubt, and gives the crew reassurance that their problem is understood. Requesting and providing clarification, paraphrasing, confirming and acknowledging all play a key role in such exchanges
Accretion rate - the speed at which ice is accumulating; it is also referred to as the accumulation rate or build-up rate
To stop doing something or stop a process that you had intended to do or had already started to do, especially a take-off or landing: take-off must be aborted before V1.
Airborne Collision Avoidance System: an aircraft system using Secondary Surveillance Radar (SSR) transponder signals, which operates independently of ground equipment to alert the flight crew about conflicting aircraft.