A clandestine subversive organization working within a country to further an invading enemy's military and political aims.
[First applied in 1936 to rebel sympathizers inside Madrid when four columns of rebel troops were attacking that city.]
fifth colum·nism (kŏləm-nĭz′əm) n.
fifth columnist n.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 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.