stiff upper lip

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An attitude of determined endurance or restraint in the face of adversity.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun idiomatic The quality of being resolute and showing self-restraint, stereotypically associated with the British; especially as keep a stiff upper lip.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun self-restraint in the expression of emotion (especially fear or grief)