The act or process of washing or rinsing with a stream of water, often used to remove debris or unwanted material.
The sluicing of the gold-bearing gravel was an essential step in the mining process.
(Linguistics) An elliptical construction in which all but the interrogative word or phrase is omitted from a clause, typically leaving a wh-word followed by an auxiliary.
In the sentence "Someone left, but I don't know who," the missing material after "who" is recovered by sluicing.