A funambulist is a tight-rope walker or rope dancer.
The word comes from the Latin funambulus with the same meaning (yes, the Romans had tight-rope walkers, too: it was a popular public spectacle). It’s a compound of funis, “rope” (the source also of our funicular, a cable railway) and ambulare, “to walk”. The Latin word evolved into the standard term for the concept in the Romance languages, for example in the Italian funambolo and French funambule. Here’s an example of its use in English from the Daily News in 1896: “A Funambulist is a gentleman who ... on a rope ... turns sommersaults, leaps thro’ a ring, and plays on a fiddle while whirling like a Catharine wheel”.
The Oxford English Dictionary lists a number of compounds and derivatives, several of them marked as obsolete: funambule, funambulant and funambulator, all meaning “a tight-rope walker”, the verb funambulate, the noun funambulation, “the action of walking on a rope”, and adjectives funambulatory and funambulic.
The word can also be used in a figurative sense to mean somebody who is mentally agile. And the original Latin word also turns up in Funambulus, the name of a genus of (presumably acrobatic) Indian palm squirrels.