flagging vs tailing off

flagging

noun
  • A pavement or sidewalk of flagstones; flagstones, collectively. 

  • The skewing or bending of the upper part of a television picture due to imperfect synchronization of the video signal. 

  • Use of a handkerchief code or analogous display to signal sexual interests. 

  • The process by which something flags or tires. 

adj
  • Becoming tired or less dynamic; declining in strength; dwindling. 

tailing off

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