Sentence:  But as every well-brought-up prince was expected to kill a <WSD>dragon</WSD>, and rescue a princess, the <WSD>dragons</WSD> grew fewer and fewer till it was often quite hard for a princess to find a dragon to be rescued from. 
Meaning of the word marked with <WSD> tags:  In Western mythology, a gigantic beast, typically reptilian with leathery bat-like wings, lion-like claws, scaly skin and a serpent-like body, often a monster with fiery breath.