A rigorous definition of symmetries in general relativity has been given by Hall (2004).

Before giving a rigorous definition of a jet, it is useful to examine some special cases.

While the principle is fairly intuitive, it does not have a rigorous mathematical definition.

Researchers, using a rigorous definition of the disorder, say they have found that it is rare, even among college women, the group considered most susceptible.

Wisely avoiding any rigorous definition, it offered at one point:

Set theory is described as naive if it uses natural language rather than rigorous definition to describe operations on sets.

Computer science provided a rigorous definition with the introduction of polynomial time, which dates to 1965.

It can be given a completely rigorous, formal definition.

There is no universally agreed or rigorous definition of a metalloid.

I find it hard to understand a rigorous definition of entropy, but I can give you an example.