? from Latin anitergium arse-wiper
"ARSEWISPE Rider gives this word, which scarcely requires explanation, as the translation of the Latin anitergium"
1653 - The First Book of the Works of Mr. Francis Rabelais, Sir Thomas Urquhart;
see Example below
From: The Works of Mr. Francis Rabelais
Volume I. Reprinted ?
The First Book of Dr. Francis Rabelais
Chapter XIII. How Gargantuas wonderful Understanding, became known to his Father Grangousier, b the Invention of a Torchecul or Wipebreech