Air mail and Junk mail

Air mail noun - Mail that is sent by air transport.

Junk mail and air mail are semantically related. in written correspondence topic. In some cases you can use "Junk mail" instead a noun phrase "Air mail".

Junk mail noun - Third-class mail consisting of advertising and often addressed to `resident' or `occupant'.

Air mail and junk mail are semantically related. You can use "Air mail" instead a noun phrase "Junk mail".