ac·a·rid (?k??-r?d)adj. Of, relating to, or belonging to the arachnid family Acaridae, which includes mites that infest stored food.n. An arachnid of the subclass Acari or the order Acarina, which includes the mites and ticks.[From New Latin Acaridae, family name, from Acarus, type genus, from acarus, mite, variant of acari, from Greek akari, a kind of mite that lives in cheese, probably alteration (influenced by koris, bedbug) of akar?s, too short to be cut, tiny; akin to epikarsios, cross-wise, at an angle; see sker- 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.acarid (?æk?r?d) , acaridan or acarinen (Animals) any of the small arachnids of the order Acarina (or Acari), which includes the ticks and mitesadj (Zoology) of or relating to the order Acarina Also (rare): acaridian or acaridean [C19: from acarus]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014ac?a?rid (?æk ? r?d) n. any arachnid of the order Acarina, comprising the mites and ticks. [1875?80; acar (us) + -id2] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.