shrinking violet

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

• noun A shy or retiring person.

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

• noun idiomatic A very shy person, who avoids contact with others if avoidable.

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

• noun someone who shrinks from familiarity with others