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roil (roil)
v. roiled, roil·ing, roils
v. tr.
1. To make (a liquid) turbulent or muddy or cloudy by stirring up sediment: The storm roiled the waters of the harbor.
2. To cause to be in a state of agitation or disorder: wars that roiled the continent for decades.
3. Usage Problem To put in a state of emotional agitation; rile or upset.
v. intr.
1. To move or be in a state of turbulence, especially because of an abundance of something: storm clouds roiling overhead; a stream roiling with salmon.
2. To be agitated or chaotic: when campuses were roiling with demonstrations.
3. To be vexed or upset: a person who is roiling with shame.

[Origin unknown.]

Usage Note: The literal meaning of the verb roil is “to make muddy or cloudy by stirring up sediment,” and this meaning has given rise to a number of figurative uses including “to be agitated” and “to cause to be agitated.” Not surprisingly, the synonymous verb rile actually began its existence as a variant of roil. It appears that the success of rile has actually come at the expense of roil, to the point where what would once have been unremarkable usages of roil now seem wrong to many readers. In our 2017 survey, 27 percent of the Usage Panel rejected the sentence The controversy continued to roil just two days before the primaries, in which figurative roil is used intransitively; 36 percent of the Usage Panel rejected transitive roil in the sentence The lyrics of the song roiled some Asian students, who felt they were racist, and 59 percent rejected the phrasal verb roil up in the sentence The administration's comments have roiled up the university's professors, who felt the administration was declaring war on tenure. Nor was it only in figurative use that the Panel found roil problematic. The literal, intransitive use of the word to mean “to move turbulently” in the sentence It was like wading through surf when a mountainous breaker is roiling toward you was judged unacceptable by 62 percent of the Panel. According to most dictionaries, all these uses should be acceptable. The survey results suggest then that many people see these uses of roil as malapropisms for rile. Writers who count themselves in this number can use a synonym like upset or agitate for the transitive uses or boil or roll for the intransitive ones.

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. 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:

    Indo-European Roots

    Semitic Roots

    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.