n.
a public toilet (see Images 1 and 2).
Type: 5. Frequency — Canadians use washroom to mean "public toilet" approximately 50% of the time (Boberg 2005, Boberg 2010: 116). This usage contrasts with the American "restroom" or "bathroom" or the British "lavatory", "loo", "WC", "toilet", or the more archaic "cloakroom". Though "bathroom" is quite widely used in Canada, this term usually refers to a room in a private dwelling (that usually includes a bathtub). It is conceivable that the high frequency of washroom is a preservation from an earlier more widespread North American form that, originally, may have referred to a room for actually washing one's hands and face, or even a place where one could take a bath (see, e.g., the 1864 and 1869 quotations). OED-3 lists its first attestation from 1806 Massachusetts and labels the term "chiefly N. Amer.". As Chart 1 shows, the term is most frequently used in Canada.
The term is one of the most widely recognized Canadianisms and can be found in most popular lists of Canadian terms and meanings for many decades back (see, e.g., the 1977 quotation).
See also COD-2, s.v. "washroom" (1), which is marked "esp. Cdn", not labelled in Gage-5 and ITP Nelson.
- Today's spelling is universally washroom, never wash room (see the 1880 quotation) or the more widespread 19th-century form wash-room (see the earliest quotations below).
- 1864  Entering the corridor from Bastion street, on the right hand, corner of Langley street, along the Arcade, is the Post-office department, consisting of a large room 32 ft. by 62 ft., with post-master's room, wash-room and fire-proof vault in the rear. 
- 1869  And the public will shall send cheques for $5, $10, or $100 for lodging, to pay for fitting it up, and providing a proper superintendent matron, wash-room, beds, and all other indispensable things. 
- 1874  The Basement of the wing now building is arranged as follows: a long corridor, 4 kitchens, warders dining room, laundry, store room, washrooms, fuel closets, boiler room [...] 
- 1882  The room upstairs for ladies and gentlemen has been fitted and decorated in the highest style of art. Ladies' toilet and washroom in connection. The first floor, for use of the general public, has also been beautifully refitted and redecorated; is large, lofty, and cool. 
- 1894  Adjoining the dormitories are the bathrooms and washroom, with marble basins and shining taps. A row of numbered tooth-brushes stood in a rack, and each towel hung from a numbered peg. 
- 1926  The bride had been shopping, and returning to the hotel found the door to the room locked. "Honey, honey, I'm here!" she exclaimed, but there was no answer. "Honey, honey, do open the door." Still no answer. "Honey! honey!" she shouted, and was greeted by a gruff thick voice saying: "Shay, you, thish ain't no-- hick-- beehive; thish ish a -- hic-- washroom." 
- 1933  Which of these children are mine? (There is a commotion offstage, and Fern Atkinson enters.) Fern (heading for the washroom) -- Take my advice and never slap a guy's face when he's chewing tobacco. 
- 1942  The fact that he had sense enough to give a false name, and also to keep out of sight in a washroom when detectives were looking the prisoners over before court started, suggested that he is not so crazy after all. 
- 1956  "Straight ahead and down to the Ladies washroom." (Whether you like it or not.) This should be the sign posted on the south west entrance of the Arts bldg. Many an innocent (?) boy has shot down the stairs to be confronted by the sign "Ladies only." "Pardon me, is this Physics 41?" The intricate entrance confuses not only the naive (?) engineers but even the intelligent artsmen. 
- 1977  ...Canadians ask for the washroom; Americans ask for the bathroom.
- 1985  The head on the Wolfe Island ferry, which is the responsibility of the provincial ministry of transportation and communications, appears deficient in minor ways. The men's room has neither a paper towel holder nor one for toilet paper: both now balance on a bulkhead and on the sink. And the liquid soap dispenser has been taken from the wall. On the positive side, graffiti has been sternly eradicated by an application of white paint. The women's washroom on the ferry is fine, one patron says. "Maybe they could have supplied another bar of soap, but it smells nice." 
- 1998  The library's washroom may be up to the province's building code, but a councillor says it's failing some patrons [sic!] 
- 2000  In another case last April, a woman who was breastfeeding at a Toronto restaurant was ordered by an employee to head for the washroom or leave.
She won an apology and financial compensation. The case also prompted the Ontario Human Rights Commission to revise its policy to specifically cover breastfeeding in public. 
- 2012  An Austrian artist and his latest installation project are making headlines.
Alexander Riegler installed a one-way mirror in the men's washroom at a Vienna sushi restaurant and gallery space, Dots. The mirror allows male patrons to peek into the women's restroom, reports Eater.com. 
- 2016  What are multi-gender washrooms? Multi-gender, multi-stall washrooms are also called family or unisex washrooms, and are common at public pools as family change-rooms.