means The substance that gets dissolved into a solvent to form a solution — the salt in the seawater, the sugar in the tea.

from From Latin 'solutus,' the past participle of 'solvere,' meaning 'to loosen, untie, dissolve' — built from 'se-' (apart) and 'luere' (to release). The same root unties itself into 'solve,' 'solution,' 'dissolve,' and 'absolve.' 'Solute' as a chemistry term is a modern back-formation, plucked from this old Latin verb to name the thing that's been loosened apart into another.