n. & v. (US vapor)
n. 1 moisture or another substance diffused or suspended in air, e.g. mist or smoke. 2 Physics a gaseous form of a normally liquid or solid substance (cf. GAS). 3 a medicinal agent for inhaling. 4 (in pl.) archaic a state of depression or melancholy thought to be caused by exhalations of vapour from the stomach.
v.intr. 1 rise as vapour. 2 make idle boasts or empty talk. vapour density the density of a gas or vapour relative to hydrogen etc. vapour pressure the pressure of a vapour in contact with its liquid or solid form. vapour trail a trail of condensed water from an aircraft or rocket at high altitude, seen as a white streak against the sky. vaporous adj. vaporously adv. vaporousness n. vapourer n. vapouring n. vapourish adj. vapoury adj.
[ ME f. OF vapour or L vapor steam, heat ]