- Arch's principal surmounting piece - Central part of a policy or system - Central piece atop an arch - Essential principle - Gem behind map legend is the most important part - Wedge-shaped piece occupying an arch's centre - The central or topmost stone of an arch. This in some
styles is made different in size from the other voussoirs, or projects,
or is decorated with carving. See Illust. of Arch.
- First in importance - First in order of importance - Headmaster - Main - Most important to have a leader at school - School head - Highest in rank, authority, character, importance, or
degree; most considerable or important; chief; main; as, the principal
officers of a Government; the principal men of a state; the principal
productions of a country; the principal arguments in a case.