The setting of two things side by side to see how they differ. Comparison requires a shared axis, and naming it is the whole method.
Latin comparatio (a matching, comparison), from comparare (to compare), from com- (together) + par (equal); the noun for the act of setting things beside each other against one shared measure.
Latin par is equal, and comparison's root insists on that equal footing before anything else happens — two things are set beside each other only once some one measure has been agreed to hold for both. Skip naming that shared axis and nothing that follows is really a comparison at all.