There is no actual official documentation where word `engineering` came from but most of people believe its came from the latin word `Ingenium` that means `cleverness` and `Ingeinare` , means "To design or devise". Some also state that its came from word `Engine` means something that transform one form of engergy to one or other form energy that make job/task easier.
So Generalized defination of engineering is quest of solving problems by using science,logic and mathamatics as a tool. and so engineer is the one who do engineering as a part of fullfilling his duties.
To simpplify this duties as problems are complex and massive and one person could not master all of them. four core categories or i should write faculties has been derived and thats are Civil, Chemical, Electrical and Mechanical. and others has been derived from them as a result of some problems of each of them becomes more complex and demanded to solve by hybriding specialized knowledge and skill from multiple faculties of this core engineering fields.
Here are the most of fields of engineering classified as per its root fields.