Difficult to understand or interpret; impenetrable: "that little creature, whose innocent life had sprung, by the inscrutable decree of Providence ... out of the rank luxuriance of a guilty passion" (Nathaniel Hawthorne).
[Middle English, from Old French, from Late Latin īnscrūtābilis : in-, not; see IN-1 + scrūtārī, to scrutinize; see SCRUTINY.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 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.