schiffen

Etymology 1
Likely from.

Verb

 * 1)  to sail
 * 2) * 1912, Martin Luther, Lutherbibel von 1912, Acts 13:4 (with KJV translation)
 * "de"

- Diese nun, wie sie ausgesandt waren vom heiligen Geist, kamen sie gen Seleucia, und von da schifften sie gen Zypern.

Etymology 2
From which in  used to be synonymous with. The term originated in this jargon in central Germany in the 1830s and had already become mainstream and widespread by 1900.

An alternative theory proposes that in olden times, noble women didn't wear any undergarments, and when they needed to urinate, servants gave them a container in the form of a little ship (Schiff being the German word for ship).

Verb

 * 1)  to urinate
 * 2)  to rain heavily
 * 1)  to rain heavily

Usage notes

 * The verb may only be understood in the second sense if the subject is.
 * No meaning is likely understood in Westphalia.