the mind > emotion > suffering > dejection > melancholy > seriousness or solemnity > be serious or solemn [verb (intransitive)] > refrain from laughing (2)
to keep one's countenance: to preserve composure, refrain from expressing emotion; now esp. to refrain from laughing or smiling. So (here, or…
Predicatively: In proper order, not ruffled or disarranged. Esp. in colloquial phrase to keep a straight face (†to keep one's face straight): to…