The opposite of "equal" is "unequal", yet there is no word "unequality". Why do we use "inequality" instead? Answer The prefixes in- and un- both have the effect of negating the meaning of the word. The prefix in- comes from Latin and almost exclusively applies to words borrowed from Latin, which in many cases were borrowed from Latin with the in- prefix already attached. The prefix un- , on the other hand, is a native English prefix, and so, in general, can apply to any English adjective. The Online Etymology Dictionary tells us that inequality was borrowed from Latin (via French) with the prefix in- already attached, so we get the word with the prefix in- : 1484, "difference of rank or dignity," from O.Fr. inequalité (14c.), from M.L. inæqualitas, from inæqualis "unequal," from in- "not" + æqualis "equal" The word unequal , on the other hand, does have the same Latin root of æqualis , but the pref...