4 syllables: Ef, fi, ca, cious. Stress on ca.
ef-uh-KAY-shuhs
/ˌɛfəˈkeɪʃəs/
Efficacious is pronounced ef-uh-KAY-shuhs (/ˌɛfəˈkeɪʃəs/). It has four syllables (Ef-fi-ca-cious), with the stress on "ca". Efficacious is an adjective meaning having the desired effect or effective; able to produce the intended result. It describes substances, methods, or interventions that work as intended. In practice, it is used to evaluate the success or usefulness of a treatment, policy, or technique.
nounEfficacious is an adjective meaning having the desired effect or effective; able to produce the intended result. It describes substances, methods, or interventions that work as intended. In practice, it is used to evaluate the success or usefulness of a treatment, policy, or technique.
"The medication proved efficacious, reducing symptoms within days."
"The training program was highly efficacious at improving exam scores."
"Several researchers argued that the new policy was not as efficacious as hoped."
Pronounce it as ɪˈfɪʃ.əs. with stress on the second syllable. Start with a short 'ih' sound, then an 'FISH'‑like second syllable, followed by a schwa plus 'shəs' ending. IPA: ɪˈfɪʃ.əs. For a quick tip: say ‘ef-FISH-us’ and drop the extra vowel before the 's' smoothly. Audio reference: you can compare with dictionary entries from Cambridge or Oxford for the US/UK variants.
Common errors: misplacing stress (e.g., ef-FI-cious or eF-FI-cious) and over-pronouncing the final -ous. Another error is treating the middle 'fi' as a long vowel rather than a short /ɪ/; some speakers also run the -ci- together as 'see-əsh' rather than the /ˈfɪʃ/ segment. Correction: keep secondary stress light on the first syllable, drive the /ɪ/ in the second syllable, and end with a clear /-ʃəs/ sequence. Use slow practice with IPA cues: ɪˈfɪʃ.əs.
US/UK/AU differences: all share the /ɪ/ in the second syllable, but rhoticity can color the final vowel in connected speech in US accents, sometimes making the final /əs/ sound lighter. UK usually maintains non-rhoticity with a crisper /ɪ/ in the middle and a less pronounced ending. Australian tends toward a centralized vowel in unstressed syllables and a slightly broader mouth position for /ɪ/; the final -ous remains /əs/. Core: ɪˈfɪʃ.əs across variants; rhoticity is minimal in UK/AU, more evident in some US speech.
Two main challenges: the /ɪ/ in the second syllable followed by /f/ and /ʃ/ combination, and the fast transition between /ɪfɪ/ to /ʃəs/ in fluent speech. The cluster -ci- is pronounced as /ʃ/ plus the schwa, not /sɪ/. The final /əs/ can blur in casual speech. Practice tip: isolate the /ɪfɪ/ part, then add /ʃəs/ while keeping the teeth lightly touching for /f/ and a relaxed /ʃ/.
There are no silent letters in standard pronunciation of efficacious. Every letter contributes to the syllables: e-ff-ici-ous, with primary stress on the second syllable. The tricky part is the consonant cluster and the /ɪ/ vowel, not silent letters. If a learner encounters a variant in fast speech, you may hear lengthening or blending, but the pronunciation itself remains phonetically explicit: ɪˈfɪʃ.əs.
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Efficacious comes from Latin efficax, efficac-, meaning ‘effective, productive,’ from efficere ‘to accomplish, bring about, effect.’ The root effic- relates to effect and accomplishment, linked to the verb efficere (to bring to pass). The -acious suffix, commonly found in adjectives, indicates a characteristic or tendency. In English, efficacious entered in the 15th–16th centuries, initially in medical or technical contexts to describe treatments, remedies, or policies that produced the desired result. Over time, usage expanded beyond medicine to general effectiveness. Its phonology reflects Latin-derived stress patterns: the primary stress falls on the second syllable (ef-FI-cacious). The word has retained a formal, somewhat scholarly register, often appearing in academic writing, clinical literature, or formal policy analysis. In modern usage, efficacious is frequently contrasted with efficent or effective, though the nuances differ slightly: efficacious emphasizes the success in achieving a goal, whereas effective highlights practical success in real-world conditions, and efficient stresses resource use. The form with -cious (as in gracious, virtuous) signals a qualitative attribute rather than mere capability. First known uses appear in Early Modern English medical and philosophical texts, with broader adoption in the 19th and 20th centuries as professional discourse matured.
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💡 These words have similar meanings to "Efficacious" and can often be used interchangeably.
🔄 These words have opposite meanings to "Efficacious" and show contrast in usage.
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Words that rhyme with "Efficacious"
-ous sounds
Practice with these rhyming pairs to improve your pronunciation consistency:
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