The mark showing something has been left out. An ellipsis is honest about omission where silence is not.
Greek elleipsis (a falling short, a leaving out), from elleipein, en- (in) plus leipein (to leave).
Its root shares its second half with eclipse: both are built on leipein, to leave, one falling short in a sentence and the other falling short of light. An ellipsis marks that leaving honestly, exactly where a silence would only look like nothing happened.