Green’s Dictionary of Slang

stiff ’un n.

also stiff one

1. [early 19C+] a corpse, thus do a stiff un, to die [ext. stiff n.1 (1)].

2. one who is unconscious (esp. through drink).

3. [mid–late 19C] a heavy drinker.

4. [mid-19C+] (also stiff) a strong alcoholic drink.

5. a large, sturdy individual.

6. [late 19C] a difficult racecourse [stiff adj. (3)].

7. [late 19C] (Aus.) a general term of abuse [SE stiff formal + ext. stiff n.1 (1)] .

8. [late 19C–1950s] a forgery [stiff n.1 (4c)].

9. [late 19C+] (horseracing) usu of a horse, a second-rate, losing contender and thus an erroneous, losing wager [fig. use of stiff n.1 (1)].