The phrase "absurd idea" refers to a thought or concept that is nonsensical, illogical, or completely unrealistic. There are many synonyms for this phrase, including ludicrous, preposterous, foolish, and irrational. Other related words that convey similar meanings include crazy, insane, outrageous, and ridiculous. These descriptions are often used to express disbelief or disagreement with the concept being discussed. Additionally, the word "absurd" itself is often used in literature and drama to create humor or irony through the use of exaggerated or unrealistic situations. Overall, the many synonyms for "absurd idea" reflect the variety of ways that we can describe something that is deemed ridiculous or nonsensical.