1. 
   Air Pressure
   The weight of the atmosphere pressing down on the Earth's surface. The effect is caused by gravity. Also called 'atmospheric pressure'.
   Found op http://www.bbc.co.uk/weather/weatherwise/glossary/a.shtml
   
   
2. 
   air pressure
   The force per unit area that the air exerts on any surface in contact with it. Primarily used for articles pertaining to air pressure within a closed environment. ... (12 Dec 1998) ...
   Found op http://www.mondofacto.com/facts/dictionary?air+pressure
   
   
3. 
   Air Pressure
   See atmospheric pressure.
   Found op http://www.physicalgeography.net/physgeoglos/a.html
   
   
4. 
   airpressure
   1) Meteorologist's or motorist's concern 2) Weather factor
   Found op http://www.mijnwoordenboek.nl/EN/crossword-dictionary/airpressure/1
   
   

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