fealty vs fluctuation

fealty

noun
  • Fidelity to one's lord or master; the feudal obligation by which the tenant or vassal was bound to be faithful to his lord. 

  • The oath by which this obligation was assumed. 

fluctuation

noun
  • A wavering; unsteadiness. 

  • In medicine, a wave-like motion or undulation of a fluid in a natural or abnormal cavity (e.g. pus in an abscess), which is felt during palpation or percussion. 

  • A motion like that of waves; a moving in this and that direction. 

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