reserved

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

• adjective Designated as unavailable except for a certain purpose or user; kept in reserve.
• adjective Given to or marked by self-restraint and reticence.

from The Century Dictionary.

• Kept for another or future use; retained; kept back.
• Showing reserve in behavior; backward in communicating one's thoughts; not open, free, or frank; distant; cold; shy; coy.
• Retired; secluded.
• In decorative art, left of the color of the background, as when another color is worked upon the ground to form a new ground, the pattern being left of the first color.
• Synonyms Excepted, withheld.
• Restrained, cautious, uncommunicative, unsocial, unsociable, taciturn.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Kept for future or special use, or for an exigency.
• adjective Restrained from freedom in words or actions; backward, or cautious, in communicating one's thoughts and feelings; not free or frank.

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

• verb Simple past tense and past participle of reserve.
• adjective comparable Slow to reveal emotion or opinions.
• adjective not comparable Set aside for the use of a particular person or party.

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

• adjective marked by self-restraint and reticence
• adjective set aside for the use of a particular person or party