rotary vs rotatory

rotary

adj
  • Capable of rotation. 

  • A rotary engine revolves the heads rather than having pistons go back and forth. 

noun
  • A roundabout, traffic circle. 

  • Any of the clubs making up the international Rotary International movement for community service. 

rotatory

adj
  • of, pertaining to, or causing rotation; rotational 

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