The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix II
Semitic Roots
ENTRY:
rbc.
DEFINITION:
Common Semitic *arbac-, four, and Central Semitic noun *rubc-, fourth, quarter. 1. Common Semitic *arbac-, four. rabi, from Arabic rabc, spring, fourth. 2. Central Semitic noun *rubc-, fourth, quarter. arroba, from Arabic ar-rubc, the quarter.