going beyond what is usual or ordinary; excessive; extreme.
an extremist, as in politics, religion, fashion, etc.
(initial capital letter) Military. the British code name for intelligence gathered by decrypting German wireless communications enciphered on the Enigma machine during World War II.
a prefix occurring originally in loanwords from Latin, with the basic meaning “on the far side of, beyond.” In relation to the base to which it is prefixed, ultra-, has the senses “located beyond, on the far side of” (ultramontane; ultraviolet), “carrying to the furthest degree possible, on the fringe of” (ultraleft; ultramodern), “extremely” (ultralight); nouns to which it is added denote, in general, objects, properties, phenomena, etc., that surpass customary norms, or instruments designed to produce or deal with such things (ultramicroscope; ultrasound; ultrastructure).