All 3 Uses

rigorous
in
Jane Eyre
(Edited)

where firm fields of ice, the accumulation of centuries of winters, glazed in Alpine heights above heights, surround the pole, and concentre the multiplied rigours of extreme cold.
p. 10.9

rigours = difficulties

unconventional spelling: This is a British spelling. Americans use rigors.
A negotiation was opened through the medium of the ambassador, Sam; and after much pacing to and fro, till, I think, the said Sam's calves must have ached with the exercise, permission was at last, with great difficulty, extorted from the rigorous Sibyl, for the three to wait upon her in a body.
p. 225.7

rigorous = difficult (or strict about how things should be done)
Laws and principles are not for the times when there is no temptation: they are for such moments as this, when body and soul rise in mutiny against their rigour; stringent are they; inviolate they shall be.
p. 365.5 *

rigour = difficulty

unconventional spelling: This is a British spelling. Americans use rigor.

Definitions:

(1) (rigorous as in: we follow a rigorous procedure)
thorough and careful procedures
(2) (rigorous as in: a rigorous math class)
difficult and demanding
(3) (rigorous as in: rigorous enforcement)
strict when enforcing rules
(4) (meaning too rare to warrant focus)