solute

The solute is the substance that gets dissolved in a solution — usually the one present in the smaller amount.

• When a solid dissolves in a liquid, like salt in water, the solid is always the solute and the liquid the solvent — that part is straightforward.
• When two liquids mix to form a solution, though, it's the smaller quantity that counts as the solute, even if it seems like it should be the other way round.
• Gulab jamun syrup is a wonderfully counter-intuitive example: most of the syrup is sugar, with only a little water — yet water is still the solvent and sugar the solute, because a large amount of sugar is dissolved into a small amount of water.
• Identifying the solute correctly matters for understanding concentration too — talking about a solution being "dilute" or "concentrated" is really a statement about how much solute is present relative to the solvent.