The term 'unbroken string' can be described by two crossword solutions: STREAK (6 letters) and RUN (3 letters). A STREAK is a long, continuous series of something, such as a winning STREAK in sports or a STREAK of luck. A RUN is a period of time during which something happens, such as a RUN of bad luck or a RUN of success. Together, these two words describe an unbroken string, which is a continuous, uninterrupted sequence of events.