Green’s Dictionary of Slang

1. a mythical beast of uncertain character.

1858		Salem Advocate (IL) 27 Jan. 1/2: They shall [...] flee unto the mountains of Hepsidam, where the lion roareth and the wang-doodle mourneth for his first-born! [DA].
1861		N.Y. Times 30 Nov. n.p.: The lion roared, but the whang-doodle did not mourn.
1870		Punchinello 9 Apr. 30/1: In his own State the Ku-Klux raged, together with the fierce whang-doodle [DA].
1880		Hartford Herald (KY) 28 Apr. 1/4: Yea, verily it was once the home of the woodbine and the whang-doodle.
1920		V. Lindsay Golden Whales of Calif. 20: The rakaboor, the hellangone, / The whangdoodle, batfowl and pig.
1930		G. Milburn ‘The Big Rock Candy Mountains II’ in Hobo’s Hornbook 88: The rock and rye springs where the whangdoodle sings, / In the Big Rock Candy Mountains.
1950		Chicago Trib. 20 Mar. 22/3: Along with the gyascutus, whangdoodle, sidehill gouger, and others, [it] is one of American folklore’s great menagerie of imaginary animals [DA].
1983		‘Heat Moon’ Blue Highways 50: This boy wouldn’t sleep up here amongst the whangdoodles withouten his peace of mind.

2. an unspecified object, something one does not know the name of [fig. use of sense 1].

1889		World (N.Y.) 13 Aug. 2/1: Sound the loud whangdoodle and beat the frenzied tom-tom. Let the American Eagle scream and rejoice.
1910		Anadarko Dly Democrat 28 Mar. 1/1: Firmly, yet gently, pull the doflicker [...] put our foot on the dingfum that touches the thingumbob, press the sockdologer [...] and then yank the everlasting stuffing out of the whang-doodle.
1917		O.O. McIntyre New York Day by Day 4 Sept. [synd. col.] Some of the latest journalistic ventures [...] are called ‘Hot-Stuff’, ‘Bing!’ [...] ‘Straight from the Shoulder’ [and] ‘The Whangdoodle.
1935		A.J. Pollock Und. Speaks n.p.: Kitty, money taken from [...] gambling pot for purpose of profits, expenses, or whangdoodles at the end of a friendly game.
1977		R. Coover Public Burning (1979) 414: Who made you get a grip on your old whangdoodle insteada the problem at hand?

3. nonsense; often used in context of sermonising.

1859		Elgin Courier 9 Sept. 3/4: A ‘whang doodle,’ hard-shell preacher wound up a flaming sermon [etc.].
1882		Nat. Police Gaz. (NY) 2 Dec. 2/4: Rev. Whangdoodle Baxter, of the Austin Blue Light Tabernacle.
1893		N. Queensland Register (Townsville, Qld) 25 Jan. n.p.: [headline] Whangdoodle Baxter Lectures About Smoking.
1926		Amer. Mercury Feb. 236/2: College presidents are in the habit of defending the late usurpation of the scholastic curriculum by the [...] athletic field with the old Latin whangdoodle about a healthy mind in a healthy body. The two actually seldom go together.

4. jazz music.

1922

Edwardsville Intelligencer (IL) 14 Sept. 4/4: The Flappers’ Dictionary [...] Whangdoodle: Jazz band music.