What's the difference between "ludicrous" and "ridiculous"?
What's difference between ludicrous and ridiculous? Are they completely synonymous?
Under the entry for laughable in Merriam-Webster's Eleventh Collegiate Dictionary (2003), a note on synonyms has this side-by-side comparison of ludicrous and ridiculous:
LUDICROUS suggests absurdity that excites both laughter and scorn {a thriller with a ludicrous plot}. RIDICULOUS suggests extreme absurdity, foolishness, or contemptibility {a ridiculous display of anger}.
So the distinction between ludicrous and ridiculous, MW seems to assert, comes down to the difference between absurdity that may provoke scorn and absurdity that may provoke contempt, within a larger context in which both words involve "provoking laughter or mirth." In my experience, ludicrous tends to be used most often to describe a situation that has elements of farcical incongruity, whereas ridiculous is a more common, all-purpose term whose meaning amounts to "not to be taken seriously."
As the following Ngram chart for ludicrous (red line) versus ridiculous (blue line) for the period 1700–2005 indicates, the frequency of use of both terms in Google Books' database of published works has decreased slightly but fairly steadily for most of the past century, and the difference in frequency between the two words has remained remarkably consistent:
Both terms are used to indicate absurdity; the subtle difference is that ludicrous means amusingly so, and ridiculous means inviting ridicule or mockery.
Because M-W doesn't make a very clear distinction, at least in my mind, I think the most significant distinction is between their respective etymologies. Ridiculous comes from the same Latin word as, for instance, our deride. Ludicrous comes from the same word as the Latin word for game, and perhaps originally had some connotation of making a game or sport of something. In any event, in contemporary English, even in Merriam-Webster, significant distinction seems to be lost.
The NOAD reports the following notes:
Ludicrous applies to whatever is so incongruous that it provokes laughter or scorn ("a ludicrous suggestion that he might escape unnoticed if he dressed up as a woman"), and ridiculous implies that ridicule or mockery is the only appropriate response ("she tried to look younger, but succeeded only in making herself look ridiculous").