Why are integrals called integrals? What is the historical background for this term? 
I cannot quite see what is integral about an integral, even if we go back to the viewing it as the area under a curve.  It seems to me a strange choice of word.

It seems to be taken from the Latin word integratus taken from here (etymonline).

1630s, "to render (something) whole," from Latin integratus or integrare, past participle of integrare "make whole," from integer "whole" (see integer). Meaning "to put together parts or elements and combine them into a whole" is from 1802.

