snake doctor vs trunnion

snake doctor

noun
  • A dragonfly 

trunnion

noun
  • One of the short stubby bearings on either side of a cannon; a gudgeon. 

  • A similar rotational bearing comprising a rotating arc or ring sliding in the groove of a stationary arc, used in machinery to allow a workpiece to be moved relative to a fixed tool. 

  • A similar rotational bearing used in automotive suspensions. 

  • A shaft, held by a bearing, at each end or side of a rotatable object. 

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