Standard Lemma guide

efficacious

adj · 3 senses · updated from the 2026-07-25 local source snapshot

Definitions and examples are grouped by meaning. Pronunciation, history, word forms, translations, descendants, synonyms, antonyms, derived terms, and related words appear whenever the source provides them.

Sound

Pronunciation

Each Play button uses your device's default local English voice, or a natural local fallback. The selected voice name appears after playback. This is synthesized speech, not a source recording.

  • Received-Pronunciation: /ˌɛf.ɪˈkeɪ.ʃəs/
  • Southern-England: Recorded audio is listed in the source snapshot.
  • General-American: /ˌɛf.əˈkeɪ.ʃəs/
  • Australian: /ˌef.əˈkæɪ.ʃəs/
  • rhymes with -eɪʃəs
  • CMU ARPABET: EH2 F AH0 K EY1 SH AH0 S Digits mark lexical stress: 1 primary, 2 secondary, 0 unstressed.

1

adj

Meaning 1

Effective; possessing efficacy.

Definition source: English Wiktionary via Wiktextract

Usage: formal

Examples

  • This medicine is efficacious.

Meaning relationships

Synonyms: effective

Antonyms: inefficacious

2

adjective

Meaning 2

producing or capable of producing an intended result or having a striking effect-LewisMumford

Definition source: Princeton WordNet 3.0

Examples

  • an air-cooled motor was more effective than a witch's broomstick for rapid long-distance transportation
  • effective teaching methods
  • effective steps toward peace
  • made an effective entrance
  • his complaint proved to be effectual in bringing action
  • an efficacious law

Meaning relationships

Synonyms: effective, effectual

Antonyms: none provided

3

adjective

Meaning 3

marked by qualities giving the power to produce an intended effect-Aldous Huxley

Definition source: Princeton WordNet 3.0

Examples

  • written propaganda is less efficacious than the habits and prejudices...of the readers
  • the medicine is efficacious in stopping a cough

Meaning relationships

Synonyms: none provided

Antonyms: inefficacious

History

Etymology

From Old French efficacieux (whence -acious), from Latin efficāx (“efficacious”) + -ous, from efficere (“to effect, to accomplish”); see effect.

Across languages

Translations

29 source translations are retained for this English entry.

  • Chinese: lêng — effective — see also effective
  • Chinese Mandarin: 有效 (yǒuxiào) — effective — see also effective
  • Chinese Mandarin: 管用 (guǎnyòng) — effective — see also effective
  • Chinese Mandarin: 奏效 (zòuxiào) — effective — see also effective
  • Chinese Mandarin: 靈驗 /灵验 (língyàn) — effective — see also effective
  • Chinese Mandarin: 藥效好 /药效好 (yàoxiào hǎo) — effective — see also effective
  • Chinese Mandarin: 療效好 /疗效好 (liáoxiào hǎo) — effective — see also effective
  • Dutch: effectief — effective — see also effective
  • Dutch: efficiënt — effective — see also effective
  • Finnish: tehokas — effective — see also effective
  • French: efficace — effective — see also effective
  • German: wirksam — effective — see also effective
  • Ancient Greek: ἐνεργητικός (energētikós) — effective — see also effective
  • Ancient Greek: ἀνύσιμος (anúsimos) — effective — see also effective
  • Ido: efikiva — effective — see also effective
  • Irish: éifeachtúil — effective — see also effective
  • Latin: efficax — effective — see also effective
  • Norwegian Bokmål: effektfull — effective — see also effective
  • Russian: де́йственный (déjstvennyj) — effective — see also effective
  • Russian: эффекти́вный (effektívnyj) — effective — see also effective
  • Spanish: efectivo — effective — see also effective
  • Spanish: eficaz — effective — see also effective
  • Spanish: presentáneo — effective — see also effective
  • Swedish: effektiv — effective — see also effective
  • Swedish: verksam — effective — see also effective
  • Tatar: нәтиҗәле (näticäle) — effective — see also effective
  • Vietnamese: hữu hiệu — effective — see also effective
  • Vietnamese: có hiệu lực — effective — see also effective
  • Vietnamese: ép phê — effective — see also effective