Ultra- a. : A prefix from the Latin ultra beyond (see Ulterior), having in composition the signification beyond, on the other side, chiefly when joined with words expressing relations of place; as, ultramarine, ultramontane, ultramundane, ultratropical, etc. In other relations it has the sense of excessively, exceedingly, beyond what is common, natural, right, or proper; as, ultraconservative; ultrademocratic, ultradespotic, ultraliberal, ultraradical, etc.

Example:


Taxonomy
Enigma, intelligence, British, German, the Allies, World War II, SLU, Bletchley Park, the Enigma, the Germans, The Ultra Secret, decryption, Naval Enigma, London, cipher, U-boats, Enigma machine, traffic.

Defination from the web:
... For some time thereafter, "Ultra" was used only for intelligence from this channel. ...