The prefix equi- means “equal” or “equally.” Equi- is from the Latin prefix aequi-, which came from Latin aequus, meaning “equal.” Thus equidistant means “equally distant.” Equi- often occurs in words with Latin elements. For example, equinox means “having the night equal (to the day),” from Latin nox, “night.” Equivalent is from valere, “to be worth, amount to,” and so is literally “amounting to the same thing.”
