(Britain) Initialism of Secret Intelligence Service. / Initialism of Schengen Information System.

Initialism of second impact syndrome. / Initialism of snow immersion suffocation. / (education) Initialism of student information system. / Initialism of supervised injection site.

(informal) Clipping of sister.

forming nouns of action or process / (medicine) forming nouns of condition / forming additional nouns

plural of SI

plural of sie

(South Africa) Expressing disgust, disappointment, or annoyance.

Third-person singular simple present indicative form of sie

simple past tense and past participle of sie

A diminutive of the male given name Simon. / A diminutive of the male given name Silas.