never vs once in a while

never

adv
  • Not at any other time; not on any other occasion; not previously. 

  • Negative particle (used to negate verbs in the simple past tense; also used absolutely). 

  • At no time; on no occasion; in no circumstance. 

intj
  • A statement of defiance 

once in a while

adv
  • Occasionally; sometimes. 

How often have the words never and once in a while occurred in a corpus of books? (source: Google Ngram Viewer )