Green’s Dictionary of Slang

bullshit n.

also bull
[fig. use of SE bull + shit n., i.e. bull dung]

1. [20C+] nonsense, lies.

2. [1910s+] (also bull manure) rubbish, anything second-rate or useless.

3. [1920s+] an object or task that is seen as annoying, irritating or ‘nonsense’.

4. showing off.

5. [1970s] an argument.

6. [1970s] (US drugs) marijuana.

7. [1970s+] used metonymically to characterize a person.

In compounds

bullshit artist (n.) (also b.a., b.s. artist, bullshit artiste, …merchant, ...thrower) [ -artist sfx/merchant n.]

[1940s+] anyone with a good line of persuasive, if insincere patter.

Bullshit Castle (n.)

[1940s+] (N.Z.) Air Force headquarters, then subseq. Parliament.

In phrases

no-bullshit (adj.) [sense 1 above]

[1970s] uncompromising.