Rooms or small buildings that serve as sanctuaries or places of Christian worship; often having an altar. A chapel may be used for private worship in or attached to a church, palace, house, prison, monastery, or school. The concept includes both freestanding chapels and rooms or recesses serving as chapels in churches or other buildings. The Latin "cappella" or the French-derived "chappelle" or "chapelle" are occasionally used for "chapel" in English texts. In its original meaning, the term referred specifically to the shrine in which the kings of France preserved the cape (cloak) of St. Martin.

Source: Art and Architecture Thesaurus

http://vocab.getty.edu/page/aat/300004590