from The American Heritage® Dictionary of the English Language, 4th Edition
- prep. In approximately; about: born circa 1900.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- prep. approximately, about
from the GNU version of the Collaborative International Dictionary of English
- prep. Approximately; about; commonly abbreviated ca.; -- used especially before dates and numerical measures.
from The Century Dictionary and Cyclopedia
- About; at or near a date given, when the exact time is not known: as, circa a. d. 500. Abbreviated circ., ca., or c.
Latin circā, from circum, around (probably on the model of adverbs like intrā, within), from circus, circle; see circle.(American Heritage® Dictionary of the English Language, Fourth Edition)
From Latin circa. (Wiktionary)