Noun
motrix (plural not attested)
(rare) A female instigator or cause of something.
Where there are large powers with little ambition (which will happen sometimes, though seldom) nature may be said to have fallen short of her purposes; for she has given the machinery without the vis motrix. Henry Taylor
Industry is the vis motrix of husbandry, and therefore an ancient English writer observes, "that a single uncultivated acre is a real physical evil in any state." Walter Harte