Soluble/ˈsɑːljəbl/ Definition 1 of 2Pro Tip 1/3Scientific Usage Often used in science, especially chemistry, to describe materials mixing into liquids. Salt is also a soluble substance in water. Pro Tip 2/3Not Universal Just because something is soluble in one liquid, doesn't mean it's soluble in others. Copper sulfate is soluble in water but not in oil. Pro Tip 3/3Degrees of Solubility Solubility can vary; some substances dissolve easily while others need more time or heat. While sugar is highly soluble in water, wax is less so.