1. [n]  an official who affixes a seal to a document
2. [n]  a kind of sealing material that is used to form a hard coating on a porous surface (as a coat of paint or varnish used to size a surface)

SEALER is a 6 letter word that starts with S.

1. \Seal"er\, n.
   One who seals; especially, an officer whose duty it is to
   seal writs or instruments, to stamp weights and measures, or
   the like.
   
   

2. \Sealer\, n.
   A mariner or a vessel engaged in the business of capturing
   seals.