motrix

Etymology
A post-classical Latin female form of classical. It is used as the feminine form of in neo-Latin, as in the original of Newton's Laws of Motion: proportionalem esse vi motrici impressae ‘is proportional to the motive force applied’ formed on the agentive suffix: -tor (masculine) / -trix (feminine).

Noun

 * 1)  A female instigator or cause of something.