Grind together is a phrase that refers to the process of two objects being rubbed together in order to reduce them to smaller pieces. The term can also be used metaphorically to describe two people or groups working together in a difficult situation. The crossword solution GNASH is a verb meaning to grind the teeth together, usually in anger or frustration. This is an example of how the phrase 'grind together' can be used figuratively to describe two people or groups struggling against each other.