epigraph

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

• noun An inscription, as on a statue or building.
• noun A motto or quotation, as at the beginning of a literary composition, setting forth a theme.

from The Century Dictionary.

• To inscribe an epigraph on.
• noun An inscription cut or impressed on stone, metal, or other permanent material, as distinguished from a writing in manuscript, etc.; specifically, in archaeology, a terse inscription on a building, tomb, monument, or statue, denoting its use or appropriation, and sometimes incorporated in its scheme of ornamentation.
• noun A superscription or title at the beginning of a book, a treatise, or a part of a book.
• noun In lit., a citation from some author, or a sentence framed for the purpose, placed at the commencement of a work or of one of its separate divisions; a motto.

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

• noun Any inscription set upon a building; especially, one which has to do with the building itself, its founding or dedication.
• noun (Literature) A citation from some author, or a sentence framed for the purpose, placed at the beginning of a work or of its separate divisions; a motto.

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

• noun an inscription, especially one on a building etc
• noun a literary quotation placed at the beginning of a book etc
• noun mathematics (of a function) the set of all points lying on or above its graph

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

• noun a quotation at the beginning of some piece of writing
• noun an engraved inscription