Is it ensure, insure, or assure?
c.1300, "figure of a circle," from Old French cercle "circle, ring (for the finger); hoop of a helmet or barrel" (12c.), from Latin circulus "circular figure; small ring, hoop; circular orbit" (also source of Italian cerchio), diminutive of circus "ring" (see circus).
Replaced Old English trendel and hring. Late Old English used circul, from Latin, but only in an astronomical sense. Meaning "group of persons surrounding a center of interest" is from 1714 (it also was a secondary sense of Latin circulus); that of "coterie" is from 1640s (a sense also found in Latin circulus). To come full circle is in Shakespeare.
late 14c., cerclen, "to shape like a globe," also "to encompass or surround," from circle (n.). From c.1400 as "to set in a circular pattern;" mid-15c. as "to move in a circle." Related: Circled; circling. To circle the wagons, figuratively, "assume an alert defensive stance" is from 1969, from old Western movies.
circle cir·cle (sûr'kəl)
A ring-shaped structure or group of structures.
A line or process with every point equidistant from the center.
To take up a defensive posture or position: ''It's time to circle the wagons and suck it up,'' veteran guard Mark Bortz said/ You might say Polaroid Corp circled the wagons to repel a $3.2 billion assault
[1980s+; fr the action taken in a cowboy movie when a wagon train is threatened by hostile Indians]