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noun
1.
the number six.
2.
a group or series of six.
1650-1660
1650-60; < Late Latin hexad- (stem of hexas) < Greek hexad- (stem of hexás) unit of six, equivalent to héx six + -ad- -ad1
Related forms
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for hexad
Historical Examples
• The hexad axis is uniterminal and all the forms are open forms.

• This is the hexad axis or hexagonal axis, for which the angle of rotation is 60, or one-sixth of 360.

• In crystals of this division of the hexagonal system the principal axis is a hexad axis of symmetry.

• Perpendicular to the hexad axis are six dyad axes of two kinds and each perpendicular to a vertical plane of symmetry.

• Here there is a plane of symmetry perpendicular to the hexad axis; there is also a centre of symmetry.

• There can be only one hexad axis of symmetry in any crystal (see figs. 77-80).

• Six planes of symmetry of two kinds intersect in the hexad axis.

• Six dyad axes of two kinds are perpendicular to the hexad axis.

• No other element is here associated with the hexad axis, which is uniterminal.

British Dictionary definitions for hexad

/ˈhɛksæd/
noun
1.
a group or series of six
2.
the number or sum of six
Derived Forms
Word Origin
C17: from Greek hexas, from hex six
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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n.

1. A group or series of six.

2. An element or radical having a valence of six.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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### Word Value for hexad

16
15
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