noun
humidifier
An appliance that adds moisture to the air, commonly used in dry winter months.
冬は加湿器をつけて寝ています。
In winter I sleep with a humidifier on.
A dehumidifier, which removes moisture from the air, opposite function of 加湿器.
Compound of 加湿 (かしつ, 'humidification') + 器 (き, 'device'). The spelling 加湿機 is a variant using 機 (き, 'machine'), but 器 is more common for small appliances.