The phrase "enough to make a cat laugh" is an idiom that means something is ridiculous or absurd. There are many synonyms for this phrase such as "laughable," "ridiculous," "preposterous," "absurd," "comical," "ludicrous," "humorous," "hilarious," "far-fetched," "farcical," and "incredible." All of these words convey a sense of disbelief or incredulity, highlighting the absurdity or ridiculousness of something. As a result, they are great alternatives to the original phrase, and can be used to express the same sentiment in different ways depending on the context.