Green’s Dictionary of Slang

1. a bow-tie.

1901		St Paul Globe (MN) 13 Jan. 3/1: [advert] Exquistite Neckware [...] Neckties! [...] Batwings and Band Bows.
1907		Warren Sheaf (MN) 12 Dec. 5/4: [advert] Neckties [...] in four-in-hands, strings, batwings.
1919		Richmond Times Dispatch (VA) 5 Oct. 4/1: [advert] We have Batwings in various patterns.
1942		L. Bennett ‘Season Ticket’ in Jam. Dialect Poems 6: One cut-wey coat, / A centre-part, an bat-wing bowtie.
1961		in Webster’s Third International Dict.

2. (also bat-wing chaps) cowboy trousers.

1920		Topeka State Jrnl (KS) 20 Mar. 4/7: Some bat-wing chaps which are very popular with the cowboys for ‘show’ [...] are twelve to fifteen inches wide.
1924		W. James Drifting Cowboy (1931) 73: I [...] traded off my angora chaps for ‘bat wings’.
1932		M. Marshall Travels of Tramp-Royal 62: And wasn’t I wearing bat-wing chaps and packing a six-gun? Oh, no.
1936		R.F. Adams Cowboy Lingo 34: ‘Chaps’ made of plain leather [...] with wide flapping legs, were called ‘bat wings,’ or ‘buzzard wings’.

3. (also bat-wing door) a swinging door, e.g. in a saloon; thus usu. in pl.

1947		W.D. Overholser Buckaroo’s Code (1948) 62: Cotton came through the batwings and was almost at the bar.
1952		W.D. Overholser Fabulous Gunman 41: The batwings were flung out and the swamper sloshed a bucket of dirty water into the street.
1962		R. Serling ‘Showdown with Rance McGrew’ in New Stories from the Twilight Zone 52: He swaggered across the set to the bat-wing doors.
1979		D. Maitland Breaking Out 125: Like a real Wild West town [...] batwing doors on the bloody pubs.

4. a half-pint flask of liquor, esp. bootleg liquor.

1950

PADS n.p.: A [...] half-pint flask, especially of bootleg liquor, is called a bat wing.

5. an upper arm that is flabby or old and so hangs down, usu. in pl. [batwing adj. (2)].

2001

‘Rev. of Total Gym’ on Fitness Infomercial Rev. 🌐 The tricep exercises on the 1100 have lessened my batwings considerably and have added definition nicely.