Webster's Revised Unabridged Dictionary · 1913

Rigorous

Rigorous , adjective

[French rigoureux, Late Latin rigorosus. See Rigor.]

1.
Manifesting, exercising, or favoring rigor; allowing no abatement or mitigation; scrupulously accurate; exact; strict; severe; relentless; as, a rigorous officer of justice; a rigorous execution of law; a rigorous definition or demonstration.
He shall be thrown down the Tarpeian Rock With rigorous hands. — Shakespeare
We do not connect the scattered phenomena into their rigorous unity. — De Quincey
2.
Severe; intense; inclement; as, a rigorous winter.
3.
Violent. [Obsolete]
Rigorous uproar. — Spenser
4.
(Mathematics, Logic) Adhering scrupulously and exactly to accepted principles; hence, logically valid; as, a rigorous proof.