Green’s Dictionary of Slang

a drink, esp. of whisky.

1809		Yes or No? 46: An’ we’ll take right gude willy-wacht, For auld lang syne.
1823		Westmorland Gaz. 8 Nov. 3/2: We’ll take a right gude willy-waught / For Lowther and lang syne.
1826		Cumberland Pacquet 12 Dec. 4/4: These horny handed sons of toil — / Require a ‘right gude willie-waught’.
1846		W. Drummond Muckomachy 13: O’ strong ale good Ilk took a michty willy-wacht.
1852		Lloyds Wkly Newspaper (London) 27 June 8/3: I wad e’en ha’e ta’en a willy-waucht o’ the water.
1861		R.H. Newell Orpheus C. Kerr I 44: Auld lang syne and Scots who ha’a [...] We’ll tak’ a right gude willie wacht for muckle twa and braw chiel.
1870		Mercury (Hobart) 23 Apr. 2/5: [from the Stranraer Free Press] [...] a willy wacht.
1871		Glasgow Herald 9 May 2/2: A sterotyped blunder [...] in ‘Auld Lang Syne thus ‘We’ll take a right gude willie-waucht’ [...] but an an editor of burns ashould know that gude-willie or gude-willet [...] means good-willed or cordial, waucht a drauught; and ‘gude-willie waucht’ means a hearty drink; while ‘gude willie-wacht’ has no meaning whatever.
1884		Dundee Courier 17 Jan. 2/3: A Richt Gude Willie Waucht to the New Year.
1903		Morpeth Herald 7 Feb. 7/3: It happens to belong to Haggisland. Opportunity is taken of the natal day to feast on haggis and willie-wauchts.
1933		‘William Juniper’ True Drunkard’s Delight 227: The tipple itself may generally be known as [...] willy-wacht.
1937		Aberdeen Jrnl 2 Feb. 3/4: What is a willie-wacht? [...] the Scottish National Dictionary would be able to give the date of the earliest record of ‘a willie-waucht’.