World War is just a colloquial term coined in the early 20th century. Originally named The World War, WWI took up its name after Time coined the name World War 2. http://time.com/3195322/world-war-grey-friday/

But you're correct that there have been many world wars in the past, wikipedia has a pretty good list: http://en.wikipedia.org/wiki/World_war#Large-scale_wars_before_1914

hi! there have been a few discussions on this subject; check out these previous posts

• Georgian:Was the seven years war technically the first world war, rather than the great war of 1914-18?

• Why didn't/don't historians refer to the Seven Year War as the first world war?

• The Seven Year's War had a theater in every continent and involved all of the major powers at the time -- why don't we refer to it as World War I?

• I've heard the Seven Years' War called "The true first world war" and "world war 0" before. Is calling the conflict a world war accurate or just another case of revisionism?

• What other wars in history could be seen as a World War?

• What criteria do historians use to designate a war as a "world war"?