Green’s Dictionary of Slang

shill n.1

[abbr. Irish shillelagh, cudgel + links of the Irish and the police]

1. (also shillaluh) the penis.

[UK] ‘Rory O’More Had A Hell Of A Bore’ in Rambler’s Flash Songster 12: Now Rory, be aisy, the girls would all cry, / When first his shillaluh they did espy.

2. (US) a police officer’s truncheon.

[US]Howsley Argot: Dict. of Und. Sl.
[US]Wentworth & Flexner DAS.
[US](con. 1940s–60s) Décharné Straight from the Fridge Dad.