enantiomer

In chemistry, an enantiomer (from the Greek ἐνάντιος, opposite, and μέρος, part or portion) is one of two stereoisomers that are mirror images of each other that are "non-superposable" (not identical), much as one's left and right hands are "the same" but opposite (It can be clearly understood if you try to place your hands one over the other without touching the back or palm of the left to the same of the right. You observe that the thumb of one is always over the little-finger of the other, thus explaining the non-superimposable or non-coincident property known as chirality.)