them·self (thĕm-sĕlf, thəm-)
a. Himself or herself. Used as a singular gender-neutral reflexive pronoun to refer to the one previously mentioned or implied, especially as a substitute for generic himself: “Relationships are hard, but all the work is worth it, unless the person you're with has totally let themself go” (John Metz).
b. Used as a singular reflexive personal pronoun for someone who does not identify as either male or female. See Usage Note at they.
2. Nonstandard Themselves: “I was telling Bubber how he and my uncles owns the whole place themself” (Carson McCullers).
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.