to-name vs tropical sweet potato

to-name

noun
  • A name added to another name; surname. 

  • A name in addition to the Christian name and surname of an individual, to distinguish him or her from others of the same name and usually indicating descent, place of residence, or some personal quality or attribute. Such to-names are often employed where the same families continually intermarry, and where consequently the same name is common to many individuals. 

tropical sweet potato

noun
  • Synonym of name (yam) 

  • Synonym of white sweet potato 

How often have the words to-name and tropical sweet potato occurred in a corpus of books? (source: Google Ngram Viewer )