The term 'cause to accept or become hardened to' can be summarized by three crossword solutions: INURE, ENURE, and SET. INURE is a verb meaning to become accustomed to something unpleasant through long exposure or practice. ENURE is a verb meaning to cause something to become established or accepted. SET is a verb meaning to make something firm or rigid. Together, these words suggest that the term refers to the process of becoming accustomed to something difficult or unpleasant, and eventually accepting it as part of life.