The term ‘hypotonic solution’ refers to a solution that has a higher solute content dissolved in the solvent than that of the cells cytosol (cell fluids) which is in this fluid, so it is a relative term which depends on the concentration of solvent in the cell(or whatever you are comparing this solution to). The opposite to this is hypertonic.
I think you have it backward. The variable, in a cellular sense, is the solute concentration not the (water) solvent concentration. HyPOtonic means there’s less impermeable solute in the water medium surrounding the cell. HypERtonic is when there is a higher impermeable solute concentration in the surrounding fluid.
