expression Definition

1. The act of expressing.

Thesaurus: representation, exposition, interpretation, elucidation, explanation, articulation.
2. A look on the face that displays feelings.

Thesaurus: countenance, cast, look, appearance, air, mien, aspect, character.
3. A word or phrase.

Thesaurus: idiom, phrase, turn of phrase, locution, phraseology, wording, term.
4. The indication of feeling, eg in a manner of speaking or a way of playing music.
5. math.
A symbol or combination of symbols.

Said of a face or voice: showing no feeling.
Thesaurus: inscrutable, impassive, deadpan, straight-faced, poker-faced, phlegmatic, blank, vacuous, wooden, empty, glassy.