Immiscible

the term that describes liquids that cannot be mixed together such as water and oil. Two liquids which can be mixed together are described as being miscible.

Taken from Dictionary of Science

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In chemistry, miscibility is the property of liquids to mix in all proportions, forming a homogeneous solution. In principle, the term applies also to other phases (solids and gases), but the main focus is on the solubility of one liquid in another. Water and ethanol, for example, are miscible since they mix in all proportions.

By contrast, substances are said to be immiscible if in some proportion, they do not form a solution. For example, diethyl ether is fairly soluble in water, but these two solvents are not miscible since they are not soluble in all proportions.

Taken from Wikipedia