last word vs old hat

last word

noun
  • Concluding remark; final advice, instructions, or observation. 

  • The finest, highest, or ultimate representative of some class of objects. 

  • The final statement uttered by a person before death. 

  • A final decision or remark, or the right to make one. 

old hat

adj
  • Very familiar; common, hackneyed or out of date. 

How often have the words last word and old hat occurred in a corpus of books? (source: Google Ngram Viewer )