I think you might mean "sillier", which is the comparative form of the adjective "silly".
Some synonyms for "sillier" are:
1. "more foolish"
"Foolish" means lacking good sense or judgment. When we compare things or people in terms of being more lacking in sense, we can use "more foolish" in place of "sillier". For example, "His ideas are sillier than hers." can also be said as "His ideas are more foolish than hers."
2. "more stupid"
"Stupid" implies a lack of intelligence or the ability to think clearly. We can say "That joke is sillier than the last one." or "That joke is more stupid than the last one." to convey a similar meaning about something being less intelligent or more ridiculous.
3. "more absurd"
"Absurd" means wildly unreasonable, illogical, or inappropriate. When something seems even more outlandish or unreasonable in a comparison, we can use "more absurd". Like, "The situation became sillier as time went on." could be rephrased as "The situation became more absurd as time went on."
4. "more ridiculous"
"Ridiculous" describes something that is deserving or inviting ridicule because it is so silly or unreasonable. For instance, "His behavior is sillier in public." can also be expressed as "His behavior is more ridiculous in public."
In summary, these words can be used as synonyms for "sillier" depending on the context to convey the idea of something being more lacking in good sense, more unreasonable, or more worthy of being laughed at.