si
/siː/noun
si is spelled S-I: 2 letters and one syllable. It appears 15 times per million words in written English, the 5,407th most frequent word form (wordfreq, 2021 data, counting Si, the name). As a noun, si means “A syllable used in solfège to represent the seventh note of a major scale” (English Wiktionary, September 2026). The plural of si is sis.
How many letters and syllables are in si?
| Letters | 2: S-I |
|---|---|
| Syllables | 1 (from its American pronunciation) |
| In writing | 15 times per million words; the 5,407th most frequent word form |
| Wrong spellings searched | none measured in search |
| Sounds like |
Sources: letters and syllables from the English Wiktionary's hyphenation or pronunciation and the CMU Pronouncing Dictionary; written frequency: wordfreq 3.1 (a 2021 snapshot of Wikipedia, subtitles, news, books, web text and social media).
How common is si?
Si appears 15 times per million words in written English, the 5,407th most frequent word form in the list. The list counts every capitalisation together, so this includes Si, the name.
Source: written frequency: wordfreq 3.1 (a 2021 snapshot of Wikipedia, subtitles, news, books, web text and social media).
How do you pronounce si?
- /siː/
Si has one syllable (counted from its American pronunciation in the CMU Pronouncing Dictionary).
Source: English Wiktionary, dump of September 2, 2026 (CC BY-SA 4.0), through kaikki.org (Wiktextract). Recordings: LL-Q1860_(eng)-Persent101-si.wav, Wikimedia Commons (author and licence on each file's page).
Words people confuse with si
Sounds like: cee, sea, see (Wiktionary's homophone list; some hold only in some accents).
Sources: English Wiktionary (homophones, alternative spellings).
Forms of si
- sis plural
- ti
Source: English Wiktionary, dump of September 2, 2026 (CC BY-SA 4.0), through kaikki.org (Wiktextract).
What does si mean?
The meanings the English Wiktionary records, quoted as written there (source below).
noun
- 1
A syllable used in solfège to represent the seventh note of a major scale.
noun
- 1
Initialism of signal integrity.
- 2
Initialism of systems integration.
- 3
Initialism of self-injury.
- 4
Initialism of suicidal ideation.
- 5
slangInitialism of self-insertion (of the author into fan fiction).
- 6
Initialism of spark ignition.
- 7
Initialism of supporting information.
- 8
Initialism of special intelligence.
adjective
- 1
Initialism of sacroiliac.
SI joint
symbol
- 1
datedIn English entries, the orthographic digraph ⟨si⟩ pronounced as the voiced postalveolar fricative /ʒ/.
Source: English Wiktionary, dump of September 2, 2026 (CC BY-SA 4.0), through kaikki.org (Wiktextract).
Si in Spanish, French, German and Portuguese
In the sense seventh note of a major scale:
Source: English Wiktionary, dump of September 2, 2026 (CC BY-SA 4.0), through kaikki.org (Wiktextract). Translations are Wiktionary's, by sense; a linked word has its own PlainSpell page.
Where does si come from?
From Middle English si (“seventh degree or note of Guido of Arezzo's hexachordal scales”), Italian si in the solmization of Guido of Arezzo, from the initials of Latin Sāncte Iohannēs (“Saint John (the Baptist)”) in the lyrics of the scale-ascending hymn Ut queant laxis by Paulus Deacon; thus, also an initialism of Sāncte Iohannēs.
Source: English Wiktionary, dump of September 2, 2026 (CC BY-SA 4.0), through kaikki.org (Wiktextract).