Green’s Dictionary of Slang

sheila-day n.

also sheila’s day
[Sheila, generic name for black domestic servants]

(S.Afr. black) Thursday, the day that most nannies and maids are allowed off work.

[[Aus]Bell’s Life in Sydney 21 Mar. 3/3: Considering that this was ‘Sheelah’s Day,’ there was little work for the magistrates, if we except an honest Hibernian who was dancing the Polka in Market-street].
[[Aus]Bell’s Life in Sydney 28 Mar. 1/2: SHEELAH'S DAY.—In the number of appearances before the police court, the Lady Sheelah had the advantage over St. Patrick, as there were two devotees to her influence who were, however, discharged].
[SA]Drum n.d. 79: They buy most of these fashion [illeg.] on their days off — usually referred to as ‘Sheila's Day’ by the boys- when they are in town either window-shopping or going the movies.
Eng. Usage in Southern Afr. V:1 8: In Soweto, Thursday is Sheila-day, day off for the nannies .
[SA]M. Melamu ‘Bad Times, Sad Times’ in Mutloatse Forced Landing 51: It’s ‘Sheila’s Day’ Babsy gets a special dispensation [...] to share the privilege of a day off with the Jo’burg domestics.
[SA]M. Tlali Footprints in the Quag 40: Why do you think in the ‘whites only’ ‘kitchens’ there is what is known as ‘Sheila’s Day’ and we never hear of ‘John’s Day’? . . . I have never heard of ‘white “Sheila’s Day”’ either.
D. Ndlovu Sheila’s Day in Perkins (1998) 143: Domestic workers both in South Africa and the U.S. got their day off on Thursday. The day, Thursday, is called ‘Sheila’s Day’ in South Africa.
[US]Hartford Courant (CT) 30 July DO1: The show ‘Sheila’s Day’ [...] domestic workers known as ‘Sheilas’ — one [group] in Alabama in the ’50’s and ’60’s and another in Soweto.