Pediment

n. triangular form on the front of a building that creates the peak of the roof; triangular form resembling a gable located above church or window

A pediment is a classical architectural element consisting of the triangular section found above the horizontal structure (entablature), typically supported by columns. The gable end of the pediment is surrounded by the cornice moulding. The tympanum, or triangular area within the pediment, was often decorated with sculptures and reliefs demonstrating scenes of Greek and Roman mythology or allegorical figures suitable to the nature of the building being adorned..
See more at Wikipedia.org...

Noun
1. a triangular gable between a horizontal entablature and a sloping roof
(hypernym) gable, gable end, gable wall

(n.)
Originally, in classical architecture, the triangular space forming the gable of a simple roof; hence, a similar form used as a decoration over porticoes, doors, windows, etc.; also, a rounded or broken frontal having a similar position and use. See Temple.
  

The crowning top of bookcases or chests.