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 The irony of the term extension is that Disney, which pushed so hard to keep its own creations out of the public domain, is perhaps our most assiduous exploiter of, yes, the public domain. Michael Hiltzik, Los Angeles Times, 26 Dec. 2023 Securing the best surviving print of a film often required assiduous detective work. Joshua Hunt, New York Times, 29 Feb. 2024 See all Example Sentences for assiduous 

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 19 May. 2024.

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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