lose the thread vs protract

lose the thread

verb
  • To get distracted and lose track of something (one's train of thought, a conversation). 

protract

verb
  • To put off to a distant time; to delay; to defer. 

  • To draw out; to extend, especially in duration. 

  • To draw to a scale; to lay down the lines and angles of, with scale and protractor; to plot. 

  • To extend; to protrude. 

  • To use a protractor. 

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