hereat vs momentarily

hereat

adv
  • At this time; upon this event. 

  • At this; because of this. 

momentarily

adv
  • Progressively; moment by moment. 

  • In a momentary manner; for a moment or instant. 

  • In a moment or very soon; any minute now, any time now. 

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