softcover vs speller

softcover

noun
  • A book having such covers. 

adj
  • Having covers made of paper or thin cardboard; paperback. 

speller

noun
  • A book used to learn how to spell properly. 

  • A person who spells. 

  • A spell checker. 

  • A participant in a spelling bee. 

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