assiduous

adjective

as·​sid·​u·​ous ə-ˈsij-wəs 

-ˈsi-jə-

: 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.”

Did you know?

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.

Synonyms

• diligent
• engaged
• busy
• employed

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

Astronomy has lost one of its most assiduous calculators of eclipses with the passing of astronomer Fred Espenak. —Joe Rao, Space.com, 3 June 2025

At his best, McCann does an assiduous, subtle job of twining his metaphors through everyday life. —Katy Waldman, New Yorker, 19 May 2025

For Britain’s prime minister, Keir Starmer, the trade deal would offer vindication for his assiduous cultivation of Mr. Trump. —Ana Swanson, New York Times, 8 May 2025

With a push back on Wednesday night, the physical and assiduous Houston Rockets earned another battle against Stephen Curry’s Golden State Warriors. —Steven Louis Goldstein, New York Times, 2 May 2025

Word History

Etymology

Latin assiduus, from assidēre to sit beside

First Known Use

circa 1552, in the meaning defined above

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Kids Definition

assiduous

adjective

as·​sid·​u·​ous ə-ˈsij-(ə-)wəs 

: constantly attentive : diligent

assiduity

ˌas-ə-ˈd(y)ü-ət-ē

noun

assiduously adverb

assiduousness noun