neither vs not at all

neither

adv
  • Similarly not. 

pron
  • Not either one of two. 

det
  • Not one of two; not either. 

  • Not either (used with nor). 

not at all

adv
  • Not in the least. 

intj
  • Used similarly to you're welcome, as a conventional reply to an expression of gratitude. 

  • Don't worry about it (response to worry or an apology) 

How often have the words neither and not at all occurred in a corpus of books? (source: Google Ngram Viewer )