Dictionary.com
definitions

-oid

  1. a suffix meaning “resembling,” “like,” used in the formation of adjectives and nouns (and often implying an incomplete or imperfect resemblance to what is indicated by the preceding element): alkaloid; anthropoid; cardioid; cuboid; lithoid; ovoid; planetoid.
Compare -ode1.

Origin of -oid

< Greek -oeidēs, equivalent to -o- -o- + -eidēs having the form of, derivative of eîdos form
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for -oid

-oid

suffix forming adjectives, suffix forming nouns
  1. indicating likeness, resemblance, or similarityanthropoid

Word Origin for -oid

from Greek -oeidēs resembling, form of, from eidos form
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
Word Origin and History for -oid

word-forming element meaning "like, like that of, thing like a ______," from Latinized form of Greek -oeides, from eidos "form," related to idein "to see," eidenai "to know;" literally "to see," from PIE *weid-es-, from root *weid- "to see, to know" (see vision). The -o- is connective or a stem vowel from the previous element.

Online Etymology Dictionary, © 2010 Douglas Harper
-oid in Medicine

-oid

suff.
  1. Resembling; one that resembles:cancroid.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
-oid in Science

-oid

  1. A suffix meaning “like” or “resembling,” as in ellipsoid, a geometric solid that resembles an ellipse.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.