"delivery of a child by cutting through the abdomen of the mother," 1923, shortening of Caesarian section (1610s); caesar as "baby delivered by caesarian section is from 1530s. Section is used here in the literal Latin sense of "a cutting."
Supposedly from Caius Julius Caesar, who was said to have been delivered surgically, thus legend traces his cognomen to Latin caesus, past participle of caedere "to cut" (see -cide). But if this is the etymology of the name, it was likely an ancestor who was so born (Caesar's mother lived to see his triumphs and such operations would have been fatal to the woman in ancient times). Rather, caesar here may come directly from caesus.
The operation was prescribed in Rome for cases of dead mothers; the first recorded instance of it being performed on a living woman is c. 1500, but as late as the early 19c., before antiseptics and blood transfusions, it had a 50% mortality rate.