Search the Oxford English Dictionary online database. You will get not only a definition of the word or term, but also its etymological history. For definitions of military terms, the best place to look is Publication 1-02, DoD Dictionary of Military and Associated Terms, in the Joint Electronic Library, online at http://www.dtic.mil/doctrine/. Click DoD Dictionary on the right-hand side of the page. That site also allows you to search for military abbreviations and acronyms.
