emphasis (n.)

1570s, "intensity of expression," from Latin emphasis, from Greek emphasis "an appearing in, outward appearance;" in rhetoric, "significance, indirect meaning," from emphainein "to present, exhibit, display, let (a thing) be seen; be reflected (in a mirror), become visible," from assimilated form of en "in" (see en- (2)) + phainein "to show" (from PIE root *bha- (1) "to shine").

In Greek and Latin, originally a figure of expression implying, in context, more than would ordinarily be meant by the words. Hence "the mode of delivery appropriate to suggestive expression, rhetorical stress," and thence, in general, extra stress or force of voice given to the utterance of a word, phrase, or part of a word in speech as a clue that it implies something more than literal meaning. In pure Latin, significatio.