Ce·phe·id (s??f?-?d, s?f??-)n. Any of a class of intrinsically variable stars with exceptionally regular periods of light pulsation.[From Cepheus.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.cepheid (?s?phi??d) astronomyna type of variable star with a regular cycle of variations in luminosityadjrelating to or resembling a variable star with a regular cycle of variations in luminosityCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014