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 ).
[ ultra (adv. and prep.) on the far side (of), beyond, deriv. of * ult ( e ) r- located beyond ]