sincere vs single-hearted

sincere

adj
  • Genuine; meaning what one says or does; heartfelt. 

  • Meant truly or earnestly. 

single-hearted

adj
  • Having an honest heart; straightforward, free from duplicity. 

  • Devoted; unambivalent and dedicated. 

How often have the words sincere and single-hearted occurred in a corpus of books? (source: Google Ngram Viewer )