SAFE-CONDUCT is a 12 letter word that starts with S.

1. \Safe"-con"duct\, n. [Safe + conduct: cf. F.
   sauf-conduit.]
   That which gives a safe passage; either
   (a) a convoy or guard to protect a person in an enemy's
       country or a foreign country, or
   (b) a writing, pass, or warrant of security, given to a
       person to enable him to travel with safety. --Shak.
   
   

2. \Safe`-con*duct"\, v. t.
   To conduct safely; to give safe-conduct to. [Poetic]
   
         He him by all the bonds of love besought To
         safe-conduct his love.                   --Spenser.