The term 'ruin partner' can be broken down into two crossword solutions: WRACK (5 letters) and RACK (4 letters). WRACK is a verb meaning to bring to ruin or destruction, while RACK is a noun meaning a frame or stand on which objects are placed. Together, these two words form the phrase 'ruin partner, ' which is used to describe two people or things that are closely associated with each other and have a shared fate.