closet of ease

From the former euphemism do one's ease (“ease one's bowels: defecate”) and to distinguish the sense from other uses of closet (“a small, private room and [obs.] a small, private outdoor space”).

closet of ease (plural closets of ease)

1. (euphemistic, obsolete) A room used to ease one's bowels: a lavatory.
   • 1662, B. Gerbier, A Brief Description of the Principles of Building, page 27:

     A Closet of ease.

• See Thesaurus:bathroom

• closet (as a lavatory)

• do one's ease
• house of ease
• seat of ease

• Oxford English Dictionary, 1st ed. "closet, n." Oxford University Press (Oxford), 1891.