1. [v]  increase the pressure on a gas or liquid
2. [v]  increase or raise; "boost the voltage in an electrical circuit"

SUPERCHARGE is a 11 letter word that starts with S.

1. \Su`per*charge"\, v. t. [imp. & p. p.
   {Supercharged}; p. pr. & vb. n. {Supercharging}.] [Pref.
   super- + charge. Cf. {Surcharge}.] (Her.)
   To charge (a bearing) upon another bearing; as, to
   supercharge a rose upon a fess.
   
   

2. \Su`per*charge"\, n. (Her.)
   A bearing charged upon another bearing. [R.]