Also written as "q.s." Short for [quantum] satis, one of the less common [Latin abbreviations]. It means "a sufficient quantity". Mainly used when describing preparation of a [chemical] or biological/pharmaceutical reagent: to "add an [ingredient] to a QS of 500 mL" means, essentially, to keep adding something until the [product] volume is 500 mL.

As a [technical writer], I find a lot of [older] documents that have instructions like "QS with X to a final volume of y mL". This term, like "[aliquot]", should never be used as a [verb], at least according to [Dorland's Illustrated Medical Dictionary].

Note that this is not to be [confused] with "[q. suff.]", short for quantum sufficit, which means "as much as suffices". Q.suff. does not need to describe a [set] amount.

QS (idea)