To lengthen in time; extend the duration of; lengthen out.To put off to a future time; postpone.To extend in space or length: as, to prolong a straight line.Synonyms and To protract, extend, continue, draw out.To lengthen out; extend.n. A prolongation: used specifically of an extension or elongated mouthpiece or chamber on retorts for the manufacture of zinc products or for the handling of other oxids which are volatile at high temperatures.