The phrase "a rigorous subject" is correct and usable in written English.
It can be used to describe a field of study or topic that requires a high level of precision, thoroughness, and discipline.
Example: "Mathematics is often considered a rigorous subject due to its reliance on logical reasoning and proof."
Alternatives: "a demanding field" or "a challenging discipline."
The Hoosier State is the latest to be subject to a rigorous study of its indigent defense system — and the latest state shown to come up short.
The apparent reason, Professor Bellah's colleagues said this week, was that in the ardently secular canon of the hard sciences, religion was deemed an insufficiently rigorous subject for scholarly scrutiny.
Over the last few decades, RE has been built up into an important and rigorous subject – and what is shocking is how quickly it has been marginalised, because of all the changes going on in education.
"RE is a popular and academically rigorous subject, however this government's actions are resulting in fewer specialist teachers, lessons being cut and exam entries going down".
Meanwhile, the areas that have been casually dropped are the very areas of philosophy that make it a dynamic, relevant and academically rigorous subject.
Students who achieve a 2 1 or above in maths or a "rigorous science subject from a good university" could apply to have their student loan written off.
As long as you've got a first or 2 1 in maths or a rigorous science subject from a good university, you can apply".
History of art is a rigorous interdisciplinary subject that gives students the critical skills to deal with a world that is increasingly saturated with images.
The decision to allow graduates who achieve a good degree in a "rigorous science subject from a good university" to apply to have their student loan written off shows that the Tories have no qualms in admitting that some universities are stronger than others.
A greater focus on rigorous subjects tested in a rigorous way.
