A substance, such as an antibody or complement protein, that binds to a bacterium or other pathogen and causes it to become more susceptible to the action of phagocytes.
[Latin opsōnāre, to buy provisions (from Greek opsōnein, from opson, condiment, delicacy; see epi in the Appendix of Indo-European roots) + -IN.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.