Green’s Dictionary of Slang

pill v.

[pill n. (1e)]

1. in senses of rejecting or failing someone.

(a) [mid-19C–1910s] to blackball.

(b) [1900s–20s] to fail a candidate in an examination.

2. [late19C-1910s] (Aus.) to shoot dead .

In phrases

pill up (v.) [pill n. (3b); image is of ostentation, showiness]

[mid-19C] (US campus) to get dressed up.