rubidium

/ˌɹuːˈbɪd.i.əm/

//ˌɹuːˈbɪd.i.əm// noun

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

"rubidium" is a 8-letter English headword indexed on PlainSpell.

The verdict

“rubidium” is uncommon English (frequency #77,166 among 3,094 “R” headwords), classed as a noun. The kind of spelling people second-guess.

#77,166
frequency rank, English
3,094
“R” headwords

According to Wiktionary data (CC BY-SA, analyzed September 3, 2026) - The chemical element (symbol Rb) with an atomic number of 37. It is a soft, highly reactive alkali metal.

Corpus desk

Index EN-rubidium · rubidium · English

rubidium · rank #77,166 · 0 variants · 0 confusables

  • FREQ-RARE #77,166
  • LEN-LONG 8 letters
  • VOW-4 4 vowels
  • CONFUS-0 No pairs
  • VAR-0 0 variants
  • BOOK-MID 3,094
  • PHOTO-FINISH rUK

Nearest frequency peer: rUK (+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.

Long-tail ranks near “rubidium”

Sparse band: bars invert rank so rarer forms read shorter

corpus weight

What this shows Long-tail view: where “rubidium” sits against similarly uncommon English ranks.

Source FrequencyWords open word-frequency list As of September 3, 2026
Key facts for rubidium
PropertyValue
Headwordrubidium
LanguageEnglish
Part of speechNoun
IPA/ˌɹuːˈbɪd.i.əm/
Letters8
Frequency rank#77,166
Misspellings tracked0
Confusable pairs0
SourceWiktionary (kaikki.org)

Long-tail rank of “rubidium” in English

Word frequency stretches from the small set of words we reach for constantly (left) out to the long tail barely used once in a while (right).rubidiumfalls in this rarity band:

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

Scale is logarithmic (each tick is 10× rarer). Rare peers in the same band: “rUK” (#77,167), “runneth” (#77,169), “roundness” (#77,162). Among 3,094 “R” headwords, “rubidium” is #77,166. Source: FrequencyWords open word-frequency list.

Rare enough to double-check

rubidium is uncommon English at frequency #77,166 among 3,094 “R” headwords, classed as anoun, transcribed /ˌɹuːˈbɪd.i.əm/. Rarity is why readers land here mid-draft. 2 senses are on record.

rubidium doesn't appear in our generated misspelling index, suggesting the orthography follows predictable English patterns. Our confusable-pair dataset has no match for it, since no other headword is close enough in sound or shape to pair with it.

Etymologically, the entry records: A New Latin word derived by German chemist R. W. Bunsen in 1861, from Latin rūbidus (“red”) because its spectrum has two red lines. The correct English form is rubidium, spelled R-U-B-I-D-I-U-M.

Definition

  1. 1
    The chemical element (symbol Rb) with an atomic number of 37. It is a soft, highly reactive alkali metal.
  2. 2
    A single atom of this element.

Etymology

A New Latin word derived by German chemist R. W. Bunsen in 1861, from Latin rūbidus (“red”) because its spectrum has two red lines.

This word in other languages

rubidio(Español)rubidium(Français)Rubidium(Deutsch)rubídio(Português)

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 "rubidium"?
"rubidium" is spelled R-U-B-I-D-I-U-M. The IPA pronunciation is /ˌɹuːˈbɪd.i.əm/.
What does "rubidium" mean?
As a noun, "rubidium" means: The chemical element (symbol Rb) with an atomic number of 37. It is a soft, highly reactive alkali metal.
How do you pronounce "rubidium"?
The IPA (International Phonetic Alphabet) transcription for "rubidium" is /ˌɹuːˈbɪd.i.əm/. 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 "rubidium"?
A New Latin word derived by German chemist R. W. Bunsen in 1861, from Latin rūbidus (“red”) because its spectrum has two red lines. 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.

Similar English words by spelling shape

Same letter count and similar misspelling depth for "rubidium", not the corpus desk frequency band.

Same letter count

Frequency-ranked English headwords with 8 letters (nearest by frequency rank).

Rosamond#77,159sandhill#77,174Sandwell#77,175Ringgold#77,151

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

Source: FrequencyWords open word-frequency list