Green’s Dictionary of Slang

a Frenchman.

1858		Westmorland Gaz. 6 Mar. 3/5: Poetry. Le Nouveau Piff-Paff de Mossoo.
1862		Cork Examiner 8 Oct. 4/2: [headline] ‘Mossoo’ in Dublin.
1866		Dundee Courier 27 Dec. 2/2: An English Boxer Chasing a French Bully [...] The police came up [...] and Massoo was removed in custody.
1869		Man about Town 27 Nov. 92/3: Mossoo [...] might [...] avenge Waterloo by kicking the greaved shins of this representative of our national chivalry.
1873		‘Cuthbert Bede’ Little Mr. Bouncer 189: [heading] Little Mr. Bouncer Departs from Mossoo’s in Company with Alphonse [Ibid.] 192: He signified to Mossoo that he approved of his work.
1875		‘Aliph Cheem’ Lays of Ind (1905) 41: [T]his was the statesmanlike view / That was taken by each diplomatic Mossoo.
1879		‘’Arry in Parry’ in Punch 15 Nov. 217/2: Parry’s O.K., and no kid; but the Mossoos is most on ’em Mugs.
1882		G.A. Sala in Living London (1883) July 300: ‘The Mounseers’ (we call them ‘Mossoos’ nowadays) ‘sheered off’.
1884		Ally Sloper’s Half Holiday 14 June 52: [caption] Enraged Mossoo— I — I vill — I vill blow your nose.
1891		in Punch 24 Jan. 48: Men dressed as Gendarmes — ‘en gendarmes français,’ writes MOSSOO DRURIOLANE.
1897		E.E. Rogers [perf. Marie Lloyd] The French Lady’s Maid 🎵 ‘Make quick, my lady! Scoot, Moosoo / My lady’s husband vos after you’.
1898		Grantham Jrnl 29 Oct. 7/5: John Bull to Mossoo [...] I can’t have a part of the Nile I’ve won / Barred access by French red tape, / You understand what I mean, Mossoo— / From Cairo is mine to the Cape!
1900		Royal Cornwall Gaz. 15 Nov. 6/7: Mr Allchin was funny in ‘he Boxes and Massoo’.
1906		Harrington & Tate [perf. Vesta Tilley] There’s Only One London Town 🎵 Off to the land of Mamzelle and Mossoo .
1913		H.G. Van Campen ‘Life on Broadway’ in McClure’s Mag. June 78/2: That’s snappy work, Floss—unless he asks Moosoo Raoul if he is my pa. Them Frenchies don't want us cuttin’ in on their graft.
1922		Joyce Ulysses 404: Au reservoir, Mossoo.