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

Relevance

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

Police said Reyes did not provide any form of identification, and attempts to identify him were unsuccessful.

— Rafael Escalera Montoto, Arkansas Online, 23 Aug. 2026
Attempts by The Associated Press to determine who their defense attorneys were to request comment were unsuccessful.

— ABC News, ABC News, 23 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

This conflation of fundraising with oversight leads to ineffective leadership, mission drift, and significant fiscal waste, including billions in turnover costs.

— Aparna Rae, Forbes.com, 21 Aug. 2026
The Los Angeles City Council has rescinded camping bans on a dozen locations in Hollywood, Echo Park and Silver Lake at the urging of the area’s council member, who called the bans ineffective in addressing homelessness.

— Sandra McDonald, Los Angeles Times, 19 Aug. 2026