Hydra vs Xiangliu

Hydra

name
  • One of Pluto's moons. 

  • One of the Saronic Islands in the Aegean Sea. 

  • A spring constellation of the northern sky, said to resemble a serpent. It lies just south of the zodiac and contains the star Alphard. 

  • A mythological serpent with many heads, slain by Hercules as one of his twelve labours. 

Xiangliu

name
  • The moon of the dwarf planet Gonggong. 

  • A hydra-like monster which terrorized the world in prehistory. 

How often have the words Hydra and Xiangliu occurred in a corpus of books? (source: Google Ngram Viewer )