assiduous

American  

[uh-sij-oo-uhs] / əˈsɪdʒ u əs /

adjective

1. constant in application or effort; working diligently at a task; persevering; industrious; meticulous.

   an assiduous student.

   Synonyms:

   sedulous, diligent, studious

   Antonyms:

   lazy, inconstant

2. constant; unremitting.

   assiduous reading.

   Synonyms:

   persistent, tireless, continuous

   Antonyms:

   lazy, inconstant

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assiduous British  

/ əˈsɪdjʊəs /

adjective

1. hard-working; persevering

   an assiduous researcher

2. undertaken with perseverance and care

   assiduous editing

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Other Word Forms

• assiduously adverb
• assiduousness noun
• unassiduous adjective
• unassiduousness noun

Etymology

Origin of assiduous

First recorded in 1530–40; from Latin assiduus, equivalent to assid(ēre) “to sit near or beside, dwell close to” ( see assess) + -uus adjective suffix; see -ous

Explanation

If you call someone assiduous, it's a compliment. It means they're careful, methodical and very persistent. Good detectives are classically assiduous types. Assiduous comes from two Latin words: assiduus, meaning "busy incessant, continual or constant," and assidere, meaning "to sit down to" something. (Funnily enough, we also get the word sedentary, meaning someone who doesn't move around much, a lazy couch potato, from this same last word.) Although we tend to think of sedentary types as being the very opposite of assiduous ones, many assiduous activities (like writing, thinking, or detective work) are best done sitting in a chair.

Example Sentences

“For Heaven’s sake,” he wrote to Congress, “be more assiduous in getting your letters here.”

From The Wall Street Journal • Apr. 3, 2026

Powell’s assiduous outreach to his colleagues gives him a good overview of where the proverbial bodies are buried, giving colleagues ample time to voice their objections.

From Barron's • Dec. 12, 2025

As the physician Peter Lipson, an assiduous pursuer of bogus medical claims, observed back in 2009, “DSHEA, as it was written and as it was intended, facilitates the legal marketing of quackery.”

From Los Angeles Times • Oct. 17, 2025

But saying no would have been difficult too, after months of assiduous effort put into developing a good relationship with President Trump.

From BBC • Jun. 22, 2025

He also became known as the most assiduous and creative hunter of new elements in history, credited with the discovery or codiscovery of twelve transuranics.

From "Big Science" by Michael Hiltzik

Related Words

• diligent
• exacting
• indefatigable
• laborious
• scrupulous
• zealous