fi·del·i·ty (fĭ-dĕlĭ-tē, fī-)
n. pl. fi·del·i·ties
a. Faithfulness to obligations, duties, or observances.
b. The condition or behavior of engaging in sex only with one's spouse or only with one's partner in a sexual relationship.
2. Exact correspondence with fact or with a given quality, condition, or event; accuracy: the fidelity of the movie to the book.
3. The degree to which an electronic system accurately reproduces the sound or image of its input signal.
[Middle English fidelite, from Old French, from Latin fidēlitās, from fidēlis, faithful, from fidēs, faith; see bheidh- in the Appendix of Indo-European roots.]
Synonyms: fidelity, allegiance, fealty, loyalty
These nouns denote faithfulness. Fidelity implies the unfailing fulfillment of one's obligations and strict adherence to vows or promises: fidelity to one's spouse; acted in fidelity to religious laws. Allegiance is faithfulness considered as a duty: "I know no South, no North, no East, no West, to which I owe any allegiance" (Henry Clay).
Fealty, once applied to the obligation of a vassal to a feudal lord, now suggests faithfulness that one has pledged to uphold: "[The candidate] pushed his experience as an executive and professed his fealty to Democratic Party principles" (David Corn).
Loyalty implies a steadfast and devoted attachment that is not easily turned aside: loyalty to an oath; loyalty to a lifelong friend.
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.