What term describes a substance that repels water?

The term that describes a substance that repels water is hydrophobic. Hydrophobic materials do not interact favorably with water; instead, they tend to repel it. This property is often observed in oils and fats, which do not mix with water due to their molecular structure.

In contrast, hydrophilic substances have an affinity for water and readily interact with it, leading to dissolution or absorption. Amphiphilic substances possess both hydrophilic and hydrophobic characteristics, which enables them to interact with both water and oil, making them useful in emulsification processes. Oily substances generally tend to be hydrophobic, but the term "oily" does not specifically define the repelling nature towards water in the same universally understood way that "hydrophobic" does. Therefore, hydrophobic is the precise term that accurately describes a substance that repels water.