as·​sid·​u·​ous ə-ˈsij-wəs How to pronounce assiduous (audio)
: showing great care, attention, and effort : marked by careful unremitting attention or persistent application
assiduous planning
an assiduous book collector
She tended her garden with assiduous attention.
assiduously adverb
assiduousness noun

Did you know?

While assiduous means “showing great care, attention, and effort,” and in some situations may be an appropriate substitute for careful, it’s got a bit more oomph than careful in that it suggests a dogged or tireless persistence. If you are assiduous in your efforts (or work, research, analysis, training, preparations, etc.) for example, it’s implied that you’re in it for the long haul, or that you have the ability to “sit with” a task or challenge for a considerable amount of time. This makes sense given that assiduous comes from the Latin verb assidēre, meaning “to sit beside.”

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The History of Assiduous

Assiduous came to English directly from the Latin assiduus, an adjective derived from the verb assidēre "to sit beside." To the ancient Romans, assiduus carried meanings ranging from “settled or rooted in place” to “constantly present” to “persistent, unremitting." This last sense was the one borrowed into English four hundred years ago and still used today, often in complimentary phrases such as "an assiduous student" and “assiduous efforts.” In the 18th century, the word took on a mildly pejorative meaning, "exhibiting a fawning attentiveness; obsequious," when used of someone striving to please. This sense has largely passed out of use.

Choose the Right Synonym for assiduous

busy, industrious, diligent, assiduous, sedulous mean actively engaged or occupied.

busy chiefly stresses activity as opposed to idleness or leisure.

too busy to spend time with the children

industrious implies characteristic or habitual devotion to work.

industrious employees

diligent suggests earnest application to some specific object or pursuit.

very diligent in her pursuit of a degree

assiduous stresses careful and unremitting application.

assiduous practice

sedulous implies painstaking and persevering application.

a sedulous investigation of the murder

Example Sentences

They were assiduous in their search for all the latest facts and figures. The project required some assiduous planning.
Recent Examples on the Web With assiduous direction from Litton, Hough and the DSO maintained close dialogue, actively listening to each other and responding in kind. Dallas News, 7 Feb. 2022 Simon Winchester tells a remarkable and highly unlikely story about two assiduous collectors—of words rather than objects—each a character of extraordinary distinctiveness, who together helped create the Oxford English Dictionary. Daniel H. Weiss, WSJ, 18 Nov. 2022 The elder Netanyahu eschewed compromise, believing that Arabs would never, ever accept Jews and that the only way to prevent another Holocaust was through unmitigated strength and assiduous wooing of supportive publics and political leaders. Jane Eisner, Washington Post, 9 Nov. 2022 Knowledgeable and assiduous consumers are the impetus needed to push the tipping point. Michelle Williams, Forbes, 20 May 2022 Digitally savvy Ukrainians have been assiduous in their fight to bring Russians to justice for war crimes. Dominique Soguel, The Christian Science Monitor, 10 June 2022 In the end, rather than convincing us that Chernobyl was a typical nuclear accident, Mr. Plokhy’s assiduous account shows that the disaster was the product of a uniquely corrupt and inhumane political system. James B. Meigs, WSJ, 20 May 2022 The administration's assiduous efforts to ease supply chain backups at ports and internal transportation hubs can help only at the margins. John Harwood, CNN, 1 Apr. 2022 Outsider Pictures is an assiduous distributor of Spanish-language films. Justin Morgan, Variety, 10 Mar. 2022 See More

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'assiduous.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Word History


Latin assiduus, from assidēre to sit beside

First Known Use

circa 1552, in the meaning defined above

Time Traveler
The first known use of assiduous was circa 1552


Dictionary Entries Near assiduous

Cite this Entry

“Assiduous.” Dictionary, Merriam-Webster, Accessed 26 Jan. 2023.

Kids Definition


as·​sid·​u·​ous ə-ˈsij-(ə-)wəs How to pronounce assiduous (audio)
: constantly attentive : diligent
assiduously adverb
assiduousness noun

More from Merriam-Webster on assiduous

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