es·trus also oes·trus (?s?tr?s)n. The periodic state of sexual excitement in the female of most mammals, excluding humans, that immediately precedes ovulation and during which the female is most receptive to mating; heat.[New Latin, from Latin oestrus, frenzy, gadfly, from Greek oistros; see eis- in Indo-European roots.]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.estrus (??str?s; ?i?str?s) n (Zoology) the usual US spelling of oestrus ?estrous, ?estrual adjCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014es?trus (??s tr?s) n. a recurring period of maximum sexual receptivity in most female mammals other than humans; heat. [1885?90;