noontime vs twelve o'clock

noontime

noun
  • Approximately noon. 

  • Noon. 

  • The time at which something peaks in some way (e.g., in vitality, in influence, in reknown) (by analogy with the waxing of the sun each day). 

twelve o'clock

noun
  • The start of the thirteenth hour of the day; noon (noontime); 12:00 p.m. (12:00). 

  • A position straight ahead (horizontal clock orientation) or above (vertical clock orientation) (from the location of the 12 mark on a clock face) 

  • The start of the first hour of the day; midnight; 12:00 a.m. (00:00). 

How often have the words noontime and twelve o'clock occurred in a corpus of books? (source: Google Ngram Viewer )