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
- 2,140
- “I” headwords
- 20
- confusable pairs
According to Wiktionary data (CC BY-SA, analyzed September 3, 2026) - Abbreviation of if and only if.
Corpus desk
Index EN-iff · iff · English
iff · rank #45,443 · 0 variants · 20 confusables
- FREQ-MID #45,443
- LEN-MID 3 letters
- VOW-1 1 vowel
- CONFUS-HIGH 20 pairs
- VAR-0 0 variants
- BOOK-MID 2,140
- PHOTO-FINISH ideation
Nearest frequency peer: ideation (-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.
Frequency neighbours of confusable “iff”
Peers at similar corpus weight, separate from look-alike pairs below
- Ibanez
Ibanez
54,561 corpus weight
- ICBM
ICBM
54,560 corpus weight
- ideation
ideation
54,559 corpus weight
- iff
iff
54,558 corpus weight
- impeccably
impeccably
54,557 corpus weight
- impulsively
impulsively
54,556 corpus weight
What this shows Bars place “iff” against nearest ranked English headwords, not a reprint of the confusable-pair desk.
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) |
Corpus rank beside confusables of “iff”
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 2,140 “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.
Recorded use
Wiktionary exampleThese source excerpts show how iff appears in context. They illustrate usage; the definition above remains the entry’s reference meaning.
A rectangle is a square iff all four of its sides have the same length.
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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Similar English words by spelling shape
Same letter count and similar misspelling depth for "iff", not the corpus desk frequency band.
Same letter count
Frequency-ranked English headwords with 3 letters (nearest by frequency rank).