Real Dictionary

ultra in American English
an extremist, as in opinions held or policies favored
going beyond the usual limit; excessive; extreme, esp. in opinions
adjective: going beyond what is usual or ordinary; excessive; extreme
noun: an extremist, as in politics, religion, fashion, etc

ultra in British English
adjective: extreme or immoderate, esp in beliefs or opinions
noun: an extremist

ultra-
prefix: Ultra- is added to adjectives to form other adjectives that emphasize that something or someone has a quality to an extreme degree.

ultra- in American English
beyond, on the farther side of
prefix: 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), “carryin

ultra- in British English
prefix: beyond or surpassing a specified extent, range, or limit