From Longman Dictionary of Contemporary Englishairmailair‧mail /ˈeəmeɪl $ ˈer-/ noun [uncountable] TCMletters and packages that are sent somewhere using a plane, or the system of doing this Send the letter by airmail.
Examples from the Corpus
airmail• Overseas orders: add £1.50 for post and packing by airmail.• In 1919, Britain's first civil airmail service began.• The price includes airmail postage to everywhere in the world.• Swiftair provides an effective, economical express service and is available at post offices. £1.95 plus airmail postage.• At just £1.75 plus the regular airmail rate the savings are obvious.From Longman Business Dictionaryairmailair‧mail /ˈeəmeɪlˈer-/ (also air mail) noun [uncountable] letters that are sent by plane, or the system of doing thisan express airmail serviceAll letters are sent by airmail. 