heptad

heptad

[hep-tad]
noun
1.
the number seven.
2.
a group of seven.
3.
Chemistry. an element, atom, or group having a valence of seven.

Origin:
1650–60; < Greek heptad- (stem of heptás). See hepta-, -ad1

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World English Dictionary
heptad (ˈhɛptæd)
 
n
1.  a group or series of seven
2.  the number or sum of seven
3.  an atom or element with a valency of seven
 
[C17: from Greek heptas seven]

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