Ludicrous means something is silly enough to cause amusement. Ridiculous means it’s absurd enough to invite mockery or derision. Ludicrous has a more playful and amusing sense than ridiculous.
We use ridiculous when something is absurd enough to be laughable. Saying something is ridiculous often means you think it deserves mockery or disrespect. An 1857 guide called English Synonyms says that “Ridiculous includes an idea of contempt, which ludicrous does not convey.”
Ridiculous is also a slang term that means unbelievable or amazing. It can refer to things that are unbelievably good or unbelievably bad. For example, you could say “That concert was ridiculous!” after seeing your favorite band give a particularly good show. You could also say “That concert was ridiculous,” after seeing a show you thought was laughably bad.
Ludicrous comes from the Latin word ludic, which means playful. That said, ludicrous is Latin for sportive or a public game.
Ludicrous is used when something is silly or absurd enough to cause laughter. English Synonyms uses this example “Nothing can be more ludicrous than the attempts which a tipsy man makes to endeavor to prove to others that he is perfectly sober.” A tipsy person pretending to be sober can be funny, but they don’t necessarily cause others to feel contemptuous toward them.
Ludicrous and Ridiculous
People tend to use ludicrous and ridiculous to make the same point. They both express a sense of silliness. Other words that can be used along with or in place of ludicrous and ridiculous are foolish, preposterous, and comical.
In casual speech, people tend to use ludicrous as a more sophisticated synonym for ridiculous. An example can be found in an article by Lesley Anne Down in Soap Opera Digest: “The curtains would open and it would be just her standing in some ludicrous pose, like Aphrodite.” If ludicrous is replaced with ridiculous, the sentence still makes sense: “The curtains would open and it would be just her standing in some ridiculous pose, like Aphrodite.”