where the term of startup came from?
The Oxford English Dictionary has this definition:


  orig. U.S. A business or enterprise that is in the process of starting up, or that has just been established; a startup company, venture, etc.


[So, as I read it, their definition contains an etymology.]

They have earlier examples of the adjective, but for the noun, they have examples of "start up" from 1970 and "start-up" from 1986, but "startup" only from 2001.