Entry 1 sense Webster, 1913 osmometer /(ŏz"mŏm"ē̇*tẽr [or] ŏs"mŏm"ē̇*tẽr)/ · os·mom·e·ter · IPA 01 n. An instrument for measuring the amount of osmotic action in different liquids. 1. An instrument for measuring the amount of osmotic action in different liquids.(Physics)