The compound "tax-rate" is a modern, transparent formation from two established English words of Latin origin. "Tax" originates from the Latin verb taxare, meaning to handle or assess, which evolved through Old French to signify a compulsory levy. "Rate" derives from the Latin ratus, meaning "reckoned" or "fixed," referring to a settled proportion or standard. Combined, they create a logical and literal term where "rate" specifies the measurable proportion at which the "tax" is applied, directly reflecting the compound's function as a key fiscal metric.

Structure: tax (a compulsory payment) + rate (a measure or proportion) - tax: From Latin taxare ("to appraise, handle, censure"), via Old French taxer. In this compound, it functions as the base noun specifying the subject of the measure. - rate: From Medieval Latin rata ("fixed amount"), from Latin ratus ("reckoned, fixed"). In this compound, it functions as the head noun specifying the measure or proportion applied.