undemonstrative

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

• adjective Not disposed to expressions of feeling; reserved.

from The Century Dictionary.

• Not demonstrative or given to excited or strong expression of feeling; reserved, from modesty, diffidence, or policy: as, an undemonstrative person; undemonstrative manners.

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

• adjective not given to showing emotion or feelings; reserved or distant

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

• adjective not given to open expression of emotion