Hydrophobic/ˌhaɪdrəˈfəʊbɪk/ Definition 1 of 2Pro Tip 1/3Technical Use Used often in sciences like chemistry and physics to describe molecules or materials. The hydrophobic end of the detergent molecule avoids water. Pro Tip 2/3Material Property Describes materials that are used to repel water in various applications. Hydrophobic sprays are used to waterproof fabrics. Pro Tip 3/3Metaphoric Speech Sometimes used metaphorically to describe someone's aversion to something. He's hydrophobic about taking risks.