rapidity
/ɹəˈpɪd.ɪ.ti/
"rapidity" is a 8-letter English headword indexed on PlainSpell.
The verdict
“rapidity” is uncommon English (frequency #61,748 among 21,470 “R” headwords), classed as a noun. The kind of spelling people second-guess.
- #61,748
- frequency rank, English
- 21,470
- “R” headwords
According to Wiktionary data (CC BY-SA, analyzed May 6, 2026) - speed, swiftness; the condition of being rapid
| Property | Value |
|---|---|
| Headword | rapidity |
| Language | English |
| Part of speech | Noun |
| IPA | /ɹəˈpɪd.ɪ.ti/ |
| Letters | 8 |
| Frequency rank | #61,748 |
| Misspellings tracked | 0 |
| Confusable pairs | 0 |
| Source | Wiktionary (kaikki.org) |
Where “rapidity” sits in English frequency
Rare enough to double-check
rapidity is uncommon English at frequency #61,748 among 21,470 “R” headwords, classed as anoun, transcribed /ɹəˈpɪd.ɪ.ti/. Rarity is why readers land here mid-draft. 3 senses are on record.
No generated misspelling entries exist for rapidity in our index, suggesting the orthography follows predictable English patterns. Our confusable-pair dataset has no match for it, which usually means its spelling is distinct enough that readers don't reach for a similar-looking word instead.
Etymologically, the entry records: From rapid + -ity, from French rapidité, from Latin rapiditas. The correct English form is rapidity, spelled R-A-P-I-D-I-T-Y.
Definition
- 1speed, swiftness; the condition of being rapid
- 2A measure of velocity relative to the speed of light; defined as artanh(v), where artanh is the hyperbolic arctangent, and v = speed (with c = speed of light = 1).
- 3A measure of the velocity of a particle in a beam relative to the beam's axis
Etymology
From rapid + -ity, from French rapidité, from Latin rapiditas.
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 “rapidity”
The practical upshot for anyone who landed here from a spell-check.
- The one correct English spelling is R-A-P-I-D-I-T-Y - every other letter order is a misspelling in standard orthography.
- Say it as /ɹəˈpɪd.ɪ.ti/ (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.