1. [v]  suffer from intense heat; "we were sweltering at the beach"
2. [v]  be uncomfortably hot

SWELTER is a 7 letter word that starts with S.

1. \Swel"ter\, v. i. [imp. & p. p. {Sweltered}; p. pr. &
   vb. n. {Sweltering}.] [From {Swelt}, v. i.]
   1. To be overcome and faint with heat; to be ready to perish
      with heat. ``Sweltered cattle.'' --Coleridge.
   
   2. To welter; to soak. [Obs.] --Drayton.
   
   

2. \Swel"ter\, v. t.
   1. To oppress with heat. --Bentley.
   
   2. To exude, like sweat. [R.] --Shak.