Rare synonym for 湿度 (しつど). Used in technical or older contexts; modern Japanese almost always uses 湿度 instead.
See also: 湿度
When humidity is high, mold tends to grow.
Compound of 気 (き, 'air, atmosphere') and 湿 (しつ, 'moisture'). The exact historical derivation is uncertain; it is a rare term that has been largely replaced by 湿度.