means the answer or method that resolves a problem, or a liquid in which something is dissolved.

from From Latin solutio, from solvere 'to loosen, untie, set free' (the same verb behind 'solve' and 'dissolve'). The two modern senses share one image: something bound up that comes undone — a knotty problem loosened into an answer, or a solid loosened apart into liquid. It reached English through Old French in the late Middle Ages.