efficacious

/ˌɛf.ɪˈkeɪ.ʃəs/

//ˌɛf.ɪˈkeɪ.ʃəs// adj

By · According to Wiktionary data (CC BY-SA) ·

"efficacious" is a 11-letter English headword indexed on PlainSpell.

The verdict

“efficacious” has 13 generated spelling variants in the English index at frequency #49,890. The variants make it a useful spelling check.

#49,890
frequency rank, English
2,246
“E” headwords
13
tracked misspellings

According to Wiktionary data (CC BY-SA, analyzed September 3, 2026) - Effective; possessing efficacy.

Corpus desk

Index EN-efficacious · efficacious · English

efficacious · rank #49,890 · 13 variants · 0 confusables

  • FREQ-MID #49,890
  • LEN-MEGA 11 letters
  • VOW-6 6 vowels
  • CONFUS-0 No pairs
  • VAR-HIGH 13 variants
  • BOOK-MID 2,246
  • PHOTO-FINISH ECHR

Nearest frequency peer: ECHR (-1 rank slots)

Read with this headword: Spelling guide for this pattern

Desk codes from Wiktionary headword shape, FrequencyWords rank tier, confusable-pair count, generated misspelling depth, letter-cohort book size, and photo-finish peer. Not a difficulty grade.

Rank peers near misspelling magnet “efficacious”

Same rarity band: useful when a typo lands on a peer headword

corpus weight

What this shows “efficacious” sits among these FrequencyWords peers; misspelling depth is tracked separately in the edit-distance chart.

Source FrequencyWords open word-frequency list As of September 3, 2026
Key facts for efficacious
PropertyValue
Headwordefficacious
LanguageEnglish
Part of speechAdjective
IPA/ˌɛf.ɪˈkeɪ.ʃəs/
Letters11
Frequency rank#49,890
Misspellings tracked13
Confusable pairs0
SourceWiktionary (kaikki.org)

Frequency seat of misspelling magnet “efficacious”

This scale runs from the tiny cluster of words that carry ordinary speech (left) to the long tail of words almost nobody reaches for (right).efficaciouslands here:

#1#100#1K#10K#100K
← used constantlyrarely used →

Ticks step logarithmically, so each one marks a roughly tenfold drop in how often the word turns up. Same rarity band neighbours include “ECHR” (#49,889), “eft” (#49,891), “ejaculate” (#49,893). Among 2,246 “E” headwords, “efficacious” is #49,890. Source: FrequencyWords open word-frequency list.

A misspelling magnet

The generator records 13 spelling variants around efficacious (IPA /ˌɛf.ɪˈkeɪ.ʃəs/), anadjective. Corpus frequency is #49,890 among 2,246 “E” headwords. Dominant gloss: "Effective; possessing efficacy.".

Our generated misspelling index lists 13 likely wrong-spelling variants for efficacious, with forms such as "effciacious", "effiaccious", and "efficaccious". Each variant is a distinct typo pattern an edit-distance generator flags, typically a doubled-consonant error, a silent-letter drop, or a vowel substitution. Our confusable-pair dataset has no match for it, which typically means the spelling is too distinctive to be mistaken for another word.

Etymologically, the entry records: From Old French efficacieux, from Latin efficāx (“efficacious”) + -ous, from efficere (“to effect, to accomplish”); see effect. The correct English form is efficacious, spelled E-F-F-I-C-A-C-I-O-U-S.

Definition

  1. 1
    Effective; possessing efficacy.

Recorded use

Wiktionary examples

These source excerpts show how efficacious appears in context. They illustrate usage; the definition above remains the entry’s reference meaning.

  1. This medicine is efficacious.
  2. For, that the ordure, which continually gathers on the skin, would ſoon ſtop the pores of it, if the ſweat were not furniſht with ſome efficacious diſſolvent to open and pierce them.

Etymology

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

This word in other languages

efectivo(Español)efficace(Français)wirksam(Deutsch)

Common misspellings

Also misspelled as:

  • effciacious
  • effiaccious
  • efficaccious
  • efficaciosu
  • efficaciouss
  • efficaciuos
  • efficacoius
  • efficaicous
  • efficcacious
  • efficcaious
  • eficacious
  • efifcacious
  • feficacious

Misspelling Pattern Breakdown

How far each generated variant is from the correct spelling of efficacious - measured in single-character edits (insert, delete, or substitute a letter). Larger bars are easier to catch; one-edit slips are the sneakiest.

effciacious2effiaccious2efficaccious1efficaciosu2efficaciouss1efficaciuos2efficacoius2efficaicous2
Edit distance from "efficacious"

Definitions, pronunciation, and etymology for this entry are drawn from Wiktionary via the kaikki.org structured extract (CC BY-SA); frequency ordering uses the FrequencyWords open word-frequency list (2018 English corpus, MIT). See the methodology for how each field is sourced and updated.

Frequently Asked Questions

How do you spell "efficacious"?
"efficacious" is spelled E-F-F-I-C-A-C-I-O-U-S. The IPA pronunciation is /ˌɛf.ɪˈkeɪ.ʃəs/.
What does "efficacious" mean?
As an adjective, "efficacious" means: Effective; possessing efficacy.
What are common misspellings of "efficacious"?
Common misspellings include "effciacious", "effiaccious", "efficaccious", "efficaciosu", "efficaciouss". The correct spelling is "efficacious".
How do you pronounce "efficacious"?
The IPA (International Phonetic Alphabet) transcription for "efficacious" is /ˌɛf.ɪˈkeɪ.ʃəs/. Click the speaker icon on the pronunciation badge above to hear it spoken aloud where audio is available.
What is the origin of the word "efficacious"?
From Old French efficacieux, from Latin efficāx (“efficacious”) + -ous, from efficere (“to effect, to accomplish”); see effect. See the full etymology section above for more details.
Is PlainSpell free to use?
Yes, PlainSpell is a completely free word reference. You can look up definitions, pronunciations, confusable pairs, homophones, and spelling corrections across 5 languages without any sign-up or subscription.

Similar English words by spelling shape

Same letter count and similar misspelling depth for "efficacious", not the corpus desk frequency band.

Same letter count

Frequency-ranked English headwords with 11 letters (nearest by frequency rank).

dereliction#49,868deregulated#49,867goalscoring#49,946Goldschmidt#49,948

Similar misspelling depth

Headwords with a similar count of attested misspellings (13 here; floor ≥5).

eroticism13 variantsfondling13 variantsCrowther13 variantscrackpot13 variants

Source: Wiktionary (via kaikki.org) Structured Wiktionary extract

Source: FrequencyWords open word-frequency list