INEFFICACIOUS Synonyms: 72 Similar and Opposite Words

inefficacious

adjective

(ˌ)i-ˌne-fə-ˈkā-shəs

Definition of inefficacious

as in unsuccessful

not producing the desired result his efforts to restore the neglected houseplant back to health were belated and sadly inefficacious

Synonyms & Similar Words

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Antonyms & Near Antonyms

as in futile

producing no results an inefficacious medication for a rare form of tuberculosis

Synonyms & Similar Words

Antonyms & Near Antonyms

Example Sentences

Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.

Recent Examples of inefficacious Day — who grew up watching the spelling bee — came up with the concept of exploring the psyche of a winner with an ultimately inefficacious career in 2015 while at a UCB improv sketch-writing class. — NBC News, 6 Oct. 2020

Recent Examples of Synonyms for inefficacious

Adjective

It could not be immediately determined if Harris has an attorney who could speak on his behalf, and efforts to reach his family by phone were unsuccessful.

— ABC News, ABC News, 16 Aug. 2026
Trump met with Kim three times for denuclearization talks during his first term in office that were ultimately unsuccessful.

— Aileen Graef, CNN Money, 16 Aug. 2026

Definition of unsuccessful

Adjective

Stuart Bloom’s futile efforts to right the space-time continuum will continue.

— Rick Porter, HollywoodReporter, 14 Aug. 2026
The central legal debate in the last stretch leading up to Mangione’s trial has revolved around who will get to participate in this perhaps futile—though understandable—interpretive exercise.

— Dan Adler, Vanity Fair, 11 Aug. 2026

Definition of futile

Adjective

The idea that government, which has been defined as incompetent and inefficient for decades, could provide grocery abundance and variety better than Walmart and Costco has triggered a visceral reaction among critics.

— Nathaniel Meyersohn, CNN Money, 15 Aug. 2026
Companies would not respond to an inefficient manufacturing operation simply by purchasing more machinery.

— Eugene Litvak, Fortune, 15 Aug. 2026

Definition of inefficient

Adjective

Even the useless adults of The Shards would surely act quickly to arrest Robert with this much evidence.

— Louis Peitzman, Vulture, 13 Aug. 2026
Talarico calls Big Bend border wall 'useless' Democratic candidate James Talarico reacted to images of bulldozers at Big Bend in an X post.

— Natassia Paloma, USA Today, 11 Aug. 2026

Definition of useless

Adjective

Ironically, the authority of doctors was supremely important to medieval people, even if the treatments seem barbaric and ineffective now.

— T.M. Brown, CNN Money, 16 Aug. 2026
Sheriff Byron Roberson said deputies deployed 10 Taser probes, but some were ineffective, potentially because of the thickness of Lunceford’s construction clothing.

— Ben Wheeler, Kansas City Star, 14 Aug. 2026