Air defense and Defensive measure

Air defense noun - Defensive measures designed to destroy attacking enemy aircraft or missiles or to nullify their effectiveness.

Defensive measure and air defense are semantically related. In some cases you can use "Defensive measure" instead a noun phrase "Air defense".

Defensive measure noun - (military) military action or resources protecting a country against potential enemies.

Air defense and defensive measure are semantically related. Sometimes you can replace phrase "Air defense" with "Defensive measure", this phrases are similar.