Solute is just a few letters short of solution, a substance that is dissolved in liquid. In science classes, a solute might be part of your experiment.
Pronounced "SAHL-yoot," the noun solute has close word relatives in dissolve, soluble, and solid — all of which are rooted in the Latin word solvere, meaning "to loosen." A solute changes state when it is dissolved. In sugar water, the solute is the sugar because it changes from solid to liquid. The water is not a solute.