Conditioner (noun)

1. A substance used to improve the condition of hair or skin.
2. A device used to control the temperature or humidity of air.

Origin:

Late 19th century: from condition + -er.

Examples:

1. She uses a leave-in hair conditioner to keep her hair soft and shiny.
2. He uses a deep conditioner to repair his damaged hair.
3. The air conditioner controls the temperature and humidity of the room.
4. The conditioning unit maintains the temperature and humidity of the greenhouse.
5. The conditioning system controls the temperature and humidity of the building.