The term 'hard to open' can be summarized by the crossword solution 'STICKY'. This term is often used to describe something that is difficult to open or close due to its adhesive properties. It is usually caused by a buildup of dirt, dust, or other particles that make it difficult to move. STICKY objects can also be caused by humidity or temperature changes. In any case, the term 'hard to open' is often used to describe something that is difficult to open or close due to its adhesive properties.