iff
/ɪf ən(d)ˈəʊn.li ɪf/
"iff" is a 3-letter English headword indexed on PlainSpell.
The verdict
“iff” sits in 20 confusable pairs (corpus #45,443) as a conjunction. The look-alike neighbours are the real trap.
- #45,443
- frequency rank, English
- 17,902
- “I” headwords
- 20
- confusable pairs
According to Wiktionary data (CC BY-SA, analyzed May 6, 2026) - Abbreviation of if and only if.
Visual similarity to commonly confused words
How many letter changes separate each confused pair (Levenshtein distance, normalized).
Source: PlainSpell confusable corpus (Wiktionary, CC BY-SA).
| Property | Value |
|---|---|
| Headword | iff |
| Language | English |
| Part of speech | Conjunction |
| IPA | /ɪf ən(d)ˈəʊn.li ɪf/ |
| Letters | 3 |
| Frequency rank | #45,443 |
| Misspellings tracked | 0 |
| Confusable pairs | 20 |
| Source | Wiktionary (kaikki.org) |
Where “iff” sits in English frequency
Easy to mix with look-alikes
The spelling risk for iff is neighbouring look-alikes ("in", "is", …), not just typos; it is aconjunction pronounced /ɪf ən(d)ˈəʊn.li ɪf/. Frequency #45,443 among 17,902 “I” headwords. Gloss: "Abbreviation of if and only if.".
No misspelling variants are generated for iff in our index, a sign its spelling follows regular English conventions. It also participates in 20 confusable-pair relationships, "in", "is", "it", and more, since the words sound or look close enough that writers reach for the wrong one mid-sentence.
This entry carries no recorded etymology, leaving phoneme-to-grapheme mapping as the best guide to its spelling rather than a borrowing history. The correct English form is iff, spelled I-F-F.
Definition
- 1Abbreviation of if and only if.
This word in other languages
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
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Using “iff”
The practical upshot for anyone who landed here from a spell-check.
- The one correct English spelling is I-F-F - every other letter order is a misspelling in standard orthography.
- Say it as /ɪf ən(d)ˈəʊn.li ɪf/ (IPA); tap the speaker on the pronunciation badge to hear it where audio exists.
- Don't mix it up with “in” - see the side-by-side comparison. iff vs in
- Browse more English words and confusable pairs in the same reference. English words
Words at a similar English frequency
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.