To make certain; determine; define or reduce to precision by removing doubt, obscurity, or ambiguity; establish; prove.To find out by trial, examination, or experiment, so as to know as certain; acquire an accurate knowledge of: as, to ascertain the weight of a commodity or the purity of a metal.To make sure of; insure.To make certain or sure; certify; assure; inform.To establish with certainty; render invariable, or not subject to caprice; fix.