There are numerous synonyms for the word "sillily" that convey a similar meaning of foolishly or absurdly. Some common synonyms include foolishly, absurdly, inanely, idiotically, and ludicrously. Other options include laughably, comically, illogically, senselessly, and nonsensically. Each of these words can be used to describe behavior or actions that are deemed foolish or unreasonable. For instance, someone who laughs for no reason or makes absurd statements can be described as behaving sillily or even downright idiotically. While the specific word chosen may depend on the context or tone of the sentence, these synonyms serve as valuable alternatives to add variety and nuance to writing or conversation.