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

Examples of assiduous in a Sentence

They were assiduous in their search for all the latest facts and figures. The project required some assiduous planning.
Recent Examples on the Web At the heart of the new museum is its 60,000-piece archive, which Armstrong assembled over decades of assiduous record-keeping and tape-recording. Justin Davidson, Curbed, 20 Sep. 2023 China’s censors, usually assiduous about controlling the flow of information on the internet, appear to have done little or nothing to stop the claims of restrictions, first reported in The Wall Street Journal. Tripp Mickle, New York Times, 11 Sep. 2023 Because years of assiduous work have gone into lightening everything from the bodywork to the seat frame, this Bentley 4 ¼ Liter weighs in at a mere 3,030 pounds, including 25 pounds of fuel. Basem Wasef, Robb Report, 2 Aug. 2023 Digitally savvy Ukrainians have been assiduous in their fight to hold Russia accountable for atrocities committed since Moscow launched full-scale war. Dominique Soguel, The Christian Science Monitor, 10 June 2022 Connelly was, after all, not only responsible for assembling the bulk of Denver’s top-tier talent through astute drafting, but also played a massive role in the team setting its organizational culture of patient, assiduous roster building founded on an ethos of loyalty and family. Joel Rush, Forbes, 5 May 2023 This split in the monastic community, Buddhist clerics say, is partly due to the military’s assiduous courting of influential monks, luring them with donations and promises that soldiers, more than civilian leaders, are the true defenders of the faith. New York Times, 28 Aug. 2021 In interviews and congressional testimony, more than a half-dozen American and Ukrainian officials described an assiduous but fallible process to track U.S.-delivered weapons. Lara Jakes, New York Times, 12 May 2023 The comeback is the product of assiduous courtship. Ilya Marritz, ProPublica, 20 Apr. 2023 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'assiduous.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

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 29 Sep. 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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