The crossword solution for the term RUN...OR RUIN is DASH, which is a four-letter word. A DASH is a punctuation mark that is used to indicate a break in a sentence or to separate items in a list. It is also used to indicate an abrupt change in thought or to emphasize a point. In the context of RUN...OR RUIN, a DASH could be used to emphasize the contrast between the two words and the potential outcomes of a situation.