Other forms: funambulists
The key to remembering funambulist is "ambulate," which comes from the Latin root meaning "to walk" — in this case referring to someone who walks on a tightrope.
Funambulist isn't related to the word fun in the sense of "an enjoyable activity" — although you might find it enjoyable to learn to walk a tightrope or, if you're afraid of heights, to watch someone else walk a tightrope. The "fun" in funambulist comes from the Latin funis, or "rope."