Former name of USAAC (“United States Army Air Corps”). (now, USAF (“United States Air Force”)); Initialism of United States Army Air Service.

Former name of USAF. (United States Air Force); Initialism of United States Army Air Forces.

Archaic form of used.

simple past tense and past participle of use

The quality of being usable.

In a usable manner.

(radio) The highest frequency that allows radio waves to be reflected off the ionosphere.

plural of usage guide

(linguistics, education) A book that explains how to use a standardised language correctly and in keeping with currently accepted style, usually through the explication of what are conservatively viewed as language "errors".

(dialectal) Us. (Compare we-uns.)