What did washington mean when he wrote that the maxim "honesty is the best policy" should be applied to foreign relations?

It seems that you have missed the given choices for this sentence, but anyway here is the correct answer. What Washington meant when he wrote that the maxim "honesty is the best policy" should be applied to foreign relations is that, there was no need to be coy about U.S. intentions to avoid permanent alliances in the future.  Hope this is the answer that you are looking for.