a calculus or concretion found in the stomach or intestines of certain animals, esp. ruminants, formerly reputed to be an effective remedy for poison.

an arrangement of five objects, as trees, in a square or rectangle, one at each corner and one in the middle.

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Example Sentences

The first stop is at a chapel-size octagon of screens.

People waited for a chance to enter the octagon and pose with a championship belt slung over their shoulder.

Collins

World English Dictionary

octagon or (less commonly) octangle (ˈɒktəɡən)

—n
	a polygon having eight sides

[C17: via Latin from Greek oktagōnos, having eight angles]

octangle or (less commonly) octangle

—n

[C17: via Latin from Greek oktagōnos, having eight angles]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Etymonline

Word Origin & History

octagon

1650s, from L. octagonos, from Gk. oktagononos, lit. "eight-angled," from okta- comb. form of okto "eight" (see eight) + gonia "angle," related to gony "knee" (see knee).

Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage

Science Dictionary

octagon

(ŏk'tə-gŏn') Pronunciation Key
A polygon having eight sides.

octagonal adjective (ŏk-tāg'ə-nəl)

American Heritage

Cultural Dictionary