insidiously

/ɪnˈsɪdi.əsli/

//ɪnˈsɪdi.əsli// adv

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

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

The verdict

“insidiously” is uncommon English (frequency #85,374 among 17,902 “I” headwords), classed as an adverb. The kind of spelling people second-guess.

#85,374
frequency rank, English
17,902
“I” headwords

According to Wiktionary data (CC BY-SA, analyzed May 6, 2026) - in an insidious manner

Key facts for insidiously
PropertyValue
Headwordinsidiously
LanguageEnglish
Part of speechAdverb
IPA/ɪnˈsɪdi.əsli/
Letters11
Frequency rank#85,374
Misspellings tracked0
Confusable pairs0
SourceWiktionary (kaikki.org)

Where “insidiously” sits in English frequency

Every-word frequency runs from the handful of words we use constantly (left) to the long tail used once in a blue moon (right). insidiously lands here:

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

Scale is logarithmic (each tick is 10× rarer). Source: FrequencyWords open word-frequency list.

Rare enough to double-check

insidiously is uncommon English at frequency #85,374 among 17,902 “I” headwords, classed as anadverb, transcribed /ɪnˈsɪdi.əsli/. Rarity is why readers land here mid-draft. Gloss: "in an insidious manner".

Zero misspellings are on record for insidiously in our index, and the word's spelling is regular enough that our generator found nothing worth flagging. No confusable counterpart is on file for this word, since its spelling is unusual enough that it doesn't cluster with a lookalike.

Etymologically, the entry records: From insidious + -ly. The correct English form is insidiously, spelled I-N-S-I-D-I-O-U-S-L-Y.

Definition

  1. 1
    in an insidious manner

Etymology

From insidious + -ly.

This word in other languages

insidieusement(Français)

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 "insidiously"?
"insidiously" is spelled I-N-S-I-D-I-O-U-S-L-Y. The IPA pronunciation is /ɪnˈsɪdi.əsli/.
What does "insidiously" mean?
As an adverb, "insidiously" means: in an insidious manner
How do you pronounce "insidiously"?
The IPA (International Phonetic Alphabet) transcription for "insidiously" is /ɪnˈsɪdi.əsli/. 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 "insidiously"?
From insidious + -ly. 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.

Using “insidiously”

The practical upshot for anyone who landed here from a spell-check.

  • The one correct English spelling is I-N-S-I-D-I-O-U-S-L-Y - every other letter order is a misspelling in standard orthography.
  • Say it as /ɪnˈsɪdi.əsli/ (IPA); tap the speaker on the pronunciation badge to hear it where audio exists.
  • Browse more English words and confusable pairs in the same reference. English words

Other uncommon English words near this rank

Data Source

Wiktionary (via kaikki.org), licensed under CC BY-SA & GFDL. Word ordering uses an open word-frequency list; misspelling variants are generated by edit-distance from the correct headword.

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

Source: FrequencyWords open word-frequency list