san

noun2

1. •
   (informal, old-fashioned) A sanatorium.

   • "Haven't you heard?" said Belinda. "Joan's ill! She'd got a high temperature, and she's in bed in the San." — 1940
2. •
   An Ancient Greek letter representing /s/ (uppercase Ϻ, lowercase ϻ), originally used in some dialects instead of sigma.