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

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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

The receiving corps is still a question mark, and depending solely on De’Von Achane seems futile.

— Gladys Louise Tyler, Forbes.com, 22 Aug. 2026
Named Wilbur by the hive mind of social media, the animal blew up online after resident Jamaal Harrison posted a video to TikTok on Saturday showing his futile attempts to catch it on an e-bike.

— Fedor Zarkhin, Los Angeles Times, 21 Aug. 2026

Definition of futile

Adjective

Garcia and Vargas Bustamante both agreed that not all of the health advice available on social media is useless, predatory or incorrect.

— Carlos De Loera, Los Angeles Times, 21 Aug. 2026
If an agent queries a legacy database to decide whether to trigger an outreach sequence or prioritize an account, a flat list of static attributes is fundamentally useless to its reasoning engine.

— Filip Popovic, Forbes.com, 18 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