The Collaborative International Dictionary of English v.0.48:

Urinator \U"ri*na`tor\, n. [L., from urinari to plunge under
   water, to dive.]
   One who dives under water in search of something, as for
   pearls; a diver. [R.] --Ray.
   [1913 Webster]

WordNet (r) 3.0 (2006):

urinator
    n 1: a person who urinates [syn: pisser, urinator]