inch·worm (?nch?wûrm?)n. A caterpillar of a geometrid moth that moves by looping the body in alternate contractions and expansions. Also called looper, measuring worm, spanworm.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.inchworm (??nt??w??m) n (Animals) another name for a measuring wormCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014meas?ur?ing?worm` or meas?uring worm`, n. a geometrid moth larva that progresses by bringing the rear end of the body forward and then advancing the front end. Also called inchworm. [1835?45] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.