the number seven.
a group of seven.
Chemistry. an element, atom, or group having a valence of seven.
Origin of heptad
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Examples from the Web for heptad
Historical Examples of heptad
a group or series of seven
the number or sum of seven
an atom or element with a valency of seven
Word Origin for heptad
C17: from Greek heptas seven
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