thankless vs thoughtless

thankless

adj
  • ungrateful or unappreciative 

  • not appreciated or rewarded 

thoughtless

adj
  • Inconsiderate, inattentive. 

  • Lacking thought or consideration. 

  • Marked by or showing lack of due thought or care; careless. 

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