A substance which is in larger proportion by mass is called solvent and which is in lesser proportion is called solute. What if the volume of the substance with lesser mass is more. Will it still remain same?
The definition given by the IUPAC Gold Book
A liquid or solid phase containing more than one substance, when for convenience one (or more) substance, which is called the solvent, is treated differently from the other substances, which are called solutes. When, as is often but not necessarily the case, the sum of the mole fractions of solutes is small compared with unity, the solution is called a dilute solution. A superscript attached to the ∞ symbol for a property of a solution denotes the property in the limit of infinite dilution.
More appropriately, a solvent is the one which has the same physical state as the solution. For example when you dissolve a gas in liquid then the solution of gas in liquid resembles the same physical state as the solvent i.e. liquid.
If both solvent and solute(s) are liquids then generally proportions are taken into account i.e. one with higher proportion is solvent.
But rarely some other criterion is used you will understand when you see it.