Added 9 October 2026
efficacious
/ˌɛf.ɪˈkeɪ.ʃəs/ adjective
In Latin: efficax Wiktionary
adjective Definition from Wiktionary (CC BY-SA). Pronunciation from Wiktionary, via Kaikki.org. More about efficacious at Wordnik → Where our words come from →
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Effective; possessing efficacy. .mw-parser-output .defdate{font-size:smaller}
This medicine is efficacious.
Origin
From Old French efficacieux (whence -acious), from Latin efficāx (“efficacious”) + -ous, from efficere (“to effect, to accomplish”); see effect.
From Wiktionary, via Kaikki.org (CC BY-SA)