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 21,470 “R” headwords), classed as a noun. The kind of spelling people second-guess.

#77,166
frequency rank, English
21,470
“R” headwords

According to Wiktionary data (CC BY-SA, analyzed May 6, 2026) - The chemical element (symbol Rb) with an atomic number of 37. It is a soft, highly reactive alkali metal.

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)

Where “rubidium” sits in English frequency

Every-word frequency runs from the handful of words we use constantly (left) to the long tail used once in a blue moon (right). rubidium lands here:

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

Scale is logarithmic (each tick is 10× rarer). Source: FrequencyWords open word-frequency list.

Rare enough to double-check

rubidium is uncommon English at frequency #77,166 among 21,470 “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.

Using “rubidium”

The practical upshot for anyone who landed here from a spell-check.

  • The one correct English spelling is R-U-B-I-D-I-U-M - every other letter order is a misspelling in standard orthography.
  • Say it as /ˌɹuːˈbɪd.i.əm/ (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.

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

Source: FrequencyWords open word-frequency list