The phrase "was rotten" indicates something that is not good or has decayed. There are numerous synonyms for this phrase that can be used to describe different situations. Some of these synonyms include "decayed," "putrefied," "spoiled," "corrupt," "contaminated," "decomposed," "moldy," "rotting," "foul," "noxious," "rancid," "stale," "tainted," "damaged," and "degraded." Each of these synonyms conveys a different level of decay or contamination and can be used based on the context of the sentence and the situation being described. These synonyms are useful in making your writing more descriptive and conveying a better understanding of the situation.