Green’s Dictionary of Slang

1. honest, candid.

1913		Bismark Daily Trib. 23 Dec. 4/1: The Valley City Times-Record puts the gaff to Col. Bloom in this wise, which [...] is cold turkey talk.
1944		New Yorker 16 Sept. 19/3: Just cold-turkey business, you lousy faker! [DA].
1952		N.Y. Daily News 4 Oct. 9C: Stalin didn’t like certain cold-turkey facts Kennan reported about Russia [W&F].

2. of an idea or situation, impossible, beyond viability.

1914

‘Hugh McHugh’ You Should Worry cap. 1: In the meantime Bunch and I had passed away. ‘It's [i.e. a plan to take Tango lessons] cold turkey,’ I whispered.

3. unconscious, dead.

1920		A. Baer Says ‘Bugs’ Baer 7 Sept. [synd. col.] [heading, of a defeated boxer] Miske Cold Turkey.
1956		I. Fleming Diamonds Are Forever (1958) 132: Out, Limey, or your pal’s cold turkey.

4. emotionless.

1939		H. Miller Tropic of Capricorn (1964) 96: The haughty one with the statuesque figure is probably a cold turkey fuck.
1957		‘Weldon Hill’ Onionhead (1958) 122: Brownie was of the [...] cold-turkey school. Buy a girl a drink, kiss her, feel her leg, and say, Let’s go to a hotel.