Definition of "rigorous"

From this time onwards, the Westinghouse air brake literally went from strength to strength, and was triumphantly justified in the course of rigorous trials, both on the Pennsylvania Railroad and at Newark-on-Trent in this country.

1946 November and December, “George Westinghouse, 1846-1914”, in Railway Magazine, page 375

Economics is a messy discipline: too fluid to be a science, too rigorous to be an art. Perhaps it is fitting that economists’ most-used metric, gross domestic product (GDP), is a tangle too. GDP measures the total value of output in an economic territory. Its apparent simplicity explains why it is scrutinised down to tenths of a percentage point every month.

2013 August 3, “Boundary problems”, in The Economist, volume 408, number 8847