plunging vs rocking

plunging

noun
  • An occurrence of putting or sinking under water or other fluid. 

  • A headlong violent motion like that of a horse trying to throw its rider. 

adj
  • That descends steeply. 

  • Aimed from higher ground, as fire upon an enemy. 

  • Very low-cut. 

rocking

noun
  • The motion of something that rocks. 

  • The abrading of a copper plate with a rocker, preparatory to mezzotinting. 

  • The motion by which the design on a steel mill is transferred to a copper cylinder. 

adj
  • Excellent; great. 

  • Shaking, swaying or moving back and forth. 

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