field of endeavour

Here is a definition of " field of endeavour" from Macmillan Dictionary:
field - definition
[COUNTABLE] a subject that you study, or a type of work that you do
field of: a chemist working in the field of polymer research
a field of study/endeavour/enquiry: She has the ability to succeed in any field of endeavour.
a specialist/expert in a field: Professor Edwards is one of the main experts in his field.

I understand completely the phrase “field of study” but not with “field of endeavour/enquiry”.
To me, it seems that “endeavour” isn’t a subject that someone studies or a type of work. It is only a good character that one has not for study or research.
Could you please clarify this?

“endeavour” in that case means the activity of trying to achieve something.