Humid means with heavy wet air that makes you sweat. A humid day, humid heat, humid and still.
The reason it is unbearable is that sweat cannot evaporate in saturated air, and evaporation is how the body cools itself — so thirty degrees humid is far worse than thirty degrees dry. Relative humidity is the share of the water the air could hold at that temperature.
1adjectivehumidWith heavy wet air.
“The air in the jungle was so humid that our clothes never dried.”
humid is a quality of air.
Latin humidus means moist, from humere, to be wet. The h was added by scribes who thought it related to humus, the ground.
Proto-Indo-European
*wegʷ-
Latin
hūmidus
Old French
humide
English, today
humid
From Old French humide, from Latin hūmidus. Borrowed from Old French humide, from Latin humidus (“moist”). Via Proto-Indo-European wegʷ- (“wet”) related to English weaky.
Etymology from Wiktionary, CC BY-SA