si

si · noun¹

1. Latin · derived fromSāncte Iohannēs“Saint John (the Baptist)”
2. Italian · derived fromsi
3. Middle English · inherited fromsi“seventh degree or note of Guido of Arezzo's hexachordal scales”
4. English todaysi

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.

SI · proper noun²

1. French · borrowed fromSI“Système international d'unités”
2. English todaySI

Borrowed from French SI (“Système international d'unités”).

Si · proper noun³

From clipping of various words beginning with the syllable /saɪ/.

Si · proper noun⁴

1. Chinese · derived from泗
2. English todaySi

From the Hanyu Pinyin romanizations of the Mandarin pronunciations of Chinese 泗 (Sì), 肆 (Sì), and 姒 (Sì, “a surname, older brother's wife”).

Words from the same roots