From Bibliotheca Anonoma

Si or ti is the seventh syllable in Solresol's alphabet. It can be represented with the written or spoken 'si', the letter 's', the color violet, a rising line (in the Solresol stenography), the number 7, the musical note B (in fixed do solfège), or the seventh note of any major musical scale (in movable do solfège). It is preceded by the note la.

The word si means "yes, okay, gladly", or "agreed."

Four-syllable words beginning with the syllable si are generally related to "city, administration, government, politics, finance, and police."

The word sisi, sometimes written as SI, indicates that a verb is in the passive participle tense.

Words beginning with si that are either four syllables with a repeated syllable in them or three syllables are generally dedicated to justice, the magistracy, and the courts.

Si is sometimes replaced with ti by some with a background in english solfège.