Common Words:
* Equidistant: At the same distance from something.
* Equilateral: Having all sides equal.
* Equilibrium: A state of balance or stability.
* Equine: Relating to horses.
* Equinox: The time of year when day and night are of equal length.
* Equivalent: Having the same value or meaning.
Less Common Words:
* Equanimity: Mental calmness, composure.
* Equipotent: Having equal power.
* Equivocal: Open to more than one interpretation; ambiguous.
* Equivocate: To use ambiguous language to conceal the truth.
* Equitable: Fair and impartial.
* Equitation: The art of horsemanship.
* Equivocation: The act of using ambiguous language to deceive.
* Equip: To provide with necessary items or tools.
* Equivariant: Remaining unchanged under a particular transformation.
Scientific and Technical Words:
* Equatorial: Relating to the equator.
* Equipotential: Having the same potential.
* Equimolar: Having equal numbers of moles.
* Equipartition: The distribution of energy equally among degrees of freedom.
* Equipotential line: A line connecting points of equal potential.
This list is not exhaustive, but it gives you a good starting point for words with the "equi-" prefix.