Lord Siva is popularly known as Shankara. The word Shankara is made up of two words, namely "shanka" and "hara".  Shanka means doubt and hara means dispeller or destroyer. It also means lord. 

The word "Shankara" thus means He who dispels or destroys doubts. dispels or destroys all doubts. He rules over our disbeliefs and hesitations and establishes firm faith in us through his compelling nature. By dispelling our doubts and establishing faith, He destroys all our bondage.

Shankara or Sankara can also mean sankata + hara,  that is he who destroys or ends all difficulties. Sincere prayers to Shankara can be very effective. The Lord is easily pleased with pure devotion and responds immediately.  Siva is known for his boon giving nature, which at times causes trouble because when he is pleased he can be very generous even to the evil characters.