a. [ L. humidus, umidus, fr. humere, umere, to be moist; akin to uvidus moist, Gr. "ygro`s, Skr. uksh to wet, sprinkle, and Icel. vökr moist, and perh. to E. ox: cf. F. humide.] Containing sensible moisture; damp; moist; as, a humidair or atmosphere; somewhat wet or watery; as, humid earth; consisting of water or vapor. [1913 Webster]

Evening cloud, or humid bow. Milton. [1913 Webster]

n. The act or process of increasing the moisture content; -- usually used of gases, especially air.
Syn. -- moisturization. [ PJC ]

n. A device that increases the moisture content of the air; -- used to avoid excessive dryness in buildings, which can cause irritation to the throat. Compare dehumidifier.
Syn. -- moisturization. [ PJC ]

v. t. to render (gases, especially air) humid or to increase the moisture content of; as, We have a machine that humidifies the air in the house.
Syn. -- moisturize, make humid, make more humid. [ WordNet 1.5 ]

n. [ Cf. F. humidité. ] 1. Moisture; dampness; a moderate degree of wetness, which is perceptible to the eye or touch; -- used especially of the atmosphere, or of anything which has absorbed moisture from the atmosphere, as clothing. [ 1913 Webster ]

2. Specifically: The content of water vapor in the air, expressed as a percent of the maximum amount of water vapor that the air can hold at the given temperature; also called relative humidity. The capacity of the air to hold moisture increases with temperature, so if the temperature changes without changing the absolute content of the atmospheric moisture, the relative humidity will also change. [ PJC ]

relative humidity Same as humidity{ 2 }. [ PJC ]

☞ In hygrometrical reports (as of the United States Signal Service) complete saturation of the air by water vapor is designated by a relative humidity of 100, and its partial saturation by smaller numbers in direct proportion to the actual content of water vapor. [ 1913 Webster ]

n. Humidity. [ 1913 Webster ]