that is

adv

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

"that-is" is a 6-letter English headword indexed on PlainSpell.

The verdict

“that is” is uncommon English (outside the top frequency list), classed as an adverb. The kind of spelling people second-guess.

Unranked
below top-frequency English
7
letters

According to Wiktionary data (CC BY-SA, analyzed May 6, 2026) - In other words; that is to say. Used to introduce a clarification or explanation

Corpus desk

Index EN-that-is · that is · English

that is · unranked · 0 variants · 0 confusables

  • FREQ-UNRANKED Unranked
  • LEN-LONG 7 letters
  • VOW-2 2 vowels
  • CONFUS-0 No pairs
  • VAR-0 0 variants
  • BOOK-THIN "T" thin
  • PHOTO-UNK Peer pending

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.

Key facts for that is
PropertyValue
Headwordthat is
LanguageEnglish
Part of speechAdverb
Letters7
Misspellings tracked0
Confusable pairs0
SourceWiktionary (kaikki.org)

Where “that is” sits in English frequency

that is falls outside the top-100,000 ranked English words, the long-tail zone of technical, archaic, or low-frequency vocabulary, exactly where readers second-guess spellings most.

Beyond rank #100,000. Source: FrequencyWords open word-frequency list.

Rare enough to double-check

that is is uncommon English outside the top frequency list, classed as anadverb. Rarity is why readers land here mid-draft. Gloss: "In other words; that is to say. Used to introduce a clarification or explanation".

The misspelling generator found no plausible variants for that is, a sign its spelling follows regular English conventions. It is not paired with a close-neighbour confusable in our dataset, which tends to mean the word is visually distinctive enough to stand on its own.

Etymologically, the entry records: From Old English þæt is. The correct English form is that is, spelled T-H-A-T- -I-S.

Definition

  1. 1
    In other words; that is to say. Used to introduce a clarification or explanation

Recorded use

Wiktionary examples

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

  1. The Brazilian population is multiethnic—that is, it has many ethnicities.
  2. We have never met —not formally, that is.

Etymology

From Old English þæt is.

This word in other languages

es decir(Español)c'est-à-dire(Français)das heißt(Deutsch)isto é(Português)

Definitions, pronunciation, and etymology for this entry are drawn from Wiktionary via the kaikki.org structured extract (CC BY-SA). See the methodology for how each field is sourced and updated.

PlainSpell is rendered directly from structured Wiktionary extracts and open word-frequency lists, no number is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of May 6, 2026. Primary sources: Wiktionary (via kaikki.org) and FrequencyWords.

Frequently Asked Questions

How do you spell "that is"?
"that is" is spelled T-H-A-T- -I-S.
What does "that is" mean?
As an adverb, "that is" means: In other words; that is to say. Used to introduce a clarification or explanation
What is the origin of the word "that is"?
From Old English þæt is. 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.
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