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

Displacing the ’90s boom bap and aughts brawlers of her last album is a streak of assiduous ’80s R&B exercises that foreground her gains as a vocalist more often than her gobstopping wordplay as a rapper. —Craig Jenkins, Vulture, 26 Sep. 2025

Smith, a former C.E.O. of Madison Square Garden, was an assiduous, somewhat robotic character, who had been appointed four and a half years earlier to modernize the auction house, which was the oldest company listed on the New York Stock Exchange. —Sam Knight, New Yorker, 25 Aug. 2025

Amid this totalizing assault, the nutria’s assiduous gnawing may seem a relatively mild insult; in the state’s coastal-threat index, the nutria would come in sixth place. —Nathaniel Rich, Harpers Magazine, 20 Aug. 2025

Record sales were up, and due to his assiduous efforts, Colonel never tired of reminding Snow, all sorts of new, high-paying opportunities in radio and television were starting to open up. —Jem Aswad, Variety, 5 Aug. 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