1. Special stress laid upon, or importance attached to, anything.
2. Anything that is given great stress or importance.
3. Special and significant stress of voice placed on particular words or syllables as indicated by position, repetition, or some other indication.
4. Intensity or force of expression, action, etc.
5. Prominence, as in form or outline.
6. Etymology: from Latin emphasis, which came from Greek emphasis "significance, indirect meaning", from empha-, root of emphainein, "to present, to show, to indicate"; from en-, "in" plus phainein, "to show".

In Greek and Latin, it developed a sense of "extra stress" given to a word or phrase in speech as a clue that it implies something more than a literal meaning.