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

Her 36-year-old NFL star boyfriend was also coming off another season playing for the Kansas City Chiefs, which ended with an unsuccessful campaign for a third consecutive Super Bowl ring.

— Rachel Burchfield, InStyle, 4 July 2026
However, the efforts were unsuccessful, according to the statement.

— Matt Lavietes, NBC news, 4 July 2026

Definition of unsuccessful

Adjective

By the late 1970s, the brothers were exhausted by the work of being professional Rosenbergs, and starting to worry that the effort was futile.

— Amy Weiss-Meyer, The Atlantic, 10 July 2026
On appeal, the Crown argued the trial judge erred by declining to order a fitness assessment before considering a stay and by concluding such an assessment would be futile.

— Christina Coulter, PEOPLE, 9 July 2026

Definition of futile

Adjective

As the large inefficient buses are phased out, this would significantly reduce the capital expenditures that Lynx requires.

— Scott Maxwell, The Orlando Sentinel, 10 July 2026
By that logic, if a route is long and inefficient, platforms should simply raise drivers’ pay and pass on the fare hike to the passenger.

— Christopher S. Tang, The Conversation, 8 July 2026

Definition of inefficient

Adjective

What remains that haven’t been scavenged have decomposed to the point where DNA analysis is difficult and all but useless in Gaza, where there are no functioning laboratories able to test and compare samples.

— Bilal Shbeir, Los Angeles Times, 9 July 2026
Jennifer, for her part, is pretty sure that the information on Dennis’s burner phone is completely useless.

— Erin Qualey, Vulture, 8 July 2026

Definition of useless

Adjective

Perhaps unsurprisingly, subsequent attempts at diplomacy, led by the ailing diplomat and intellectual Benjamin Franklin, also proved ineffective.

— Sarah M.S. Pearsall, The Conversation, 2 July 2026
Skunks would rather put up with the strong scent of mothballs than leave a hospitable environment, making mothballs totally ineffective against skunks.

— Michelle Mastro, The Spruce, 1 July 2026

Definition of ineffective

Adjective

What this framework dismantles is a common and counterproductive myth—that friendships either spark instantly or are not worth pursuing.

— Wes Moss, Forbes.com, 10 July 2026
Johnson continued this week to push for his foolish and counterproductive desire to impose a $33-per-month tax on each Chicago job generated by the city’s largest private-sector employers.

— The Editorial Board, Chicago Tribune, 10 July 2026