Ludicrous comes from Latin ludicrus (probably from ludicrum ‘stage play’) + -ous. 

According to the Oxford English Dictionary (OED), the word ludicrous was first used in English in the early 1600s. The OED's earliest recorded evidence for "ludicrous" is from 1619 in the writings of Thomas Gataker.  During the 17th century and most of the 18th century the word ludicrous meant "pertaining to play or sport".  The modern sense of "ridiculous" or "provoking laughter or deserving to be laughed at" developed later, around 1782. 

Examples of "ludicrous" in a sentence: 
"To say that he did not know what was going on is ludicrous."
"It would be ludicrous if it were otherwise."
"The plot mechanics are ludicrous and tedious."
"It would be ludicrous of me to criticize any one of them." 
"This crazy award also opens the path for similar ludicrous claims." 
"Now we have both sides hurling insults at one another and coming up with more and more ludicrous claims." 
"As soon as you read the official explanations, you just know something ludicrous has taken place." 

Just the facts:

LUDICROUS Definition & Meaning - Merriam-Webster

LUDICROUS Synonyms: 157 Similar and Opposite Words | Merriam-Webster Thesaurus