equi-

Equal; equally.

Latin aequi‑, from aequus, equal.

Two things that are equiangular have equal angles; though it has other meanings, the key sense of equity is equality, fairness, and impartiality; an equipoise is a balance of forces or interests.

Other examples come from Latin words with the prefix already attached: equilateral (Latin aequilaterus, equal-sided, from latus, later‑, side), having all its sides the same length; equilibrium (Latin aequilibrium, from libra, balance), a state in which opposing forces or influences are balanced; equinox (aequinoctium, from nox, noct‑, night), the dates on which day and night are of equal length.

However, equine and its relatives come from Latin equus, horse, as does equisetum, a plant of a genus that comprises the horsetails; equip is probably from Old Norse skipa, to man a ship.