rigorous vs vigorous

i've often wondered what the difference is between these 2 words. now it is time to know the answer, once and for all.

rigorous

Pronunciation: \ˈri-g(ə-)rəs\

Function: adjective

Date: 15th century

1 : manifesting, exercising, or favoring rigor : very strict
2 a : marked by extremes of temperature or climate b : harsh, severe
3 : scrupulously accurate : precise

synonyms see rigid

— rig·or·ous·ly adverb
— rig·or·ous·ness noun

vigorous

Pronunciation: \ˈvi-g(ə-)rəs\

Function: adjective

Etymology: Middle English vigorous, vigrous, from Anglo-French, from vigour

Date: 14th century

1 : possessing vigor : full of physical or mental strength or active force : strong
2 : done with vigor : carried out forcefully and energetically

— vig·or·ous·ly adverb
— vig·or·ous·ness noun

synonyms vigorous, energetic, strenuous, lusty, nervous mean having or showing great vitality and force. vigorous further implies showing no signs of depletion or diminishing of freshness or robustness vigorous as a youth half his age. energetic suggests a capacity for intense activity energetic campaigner. strenuous suggests a preference for coping with the arduous or the challenging strenuous life on an oil rig. lusty implies exuberant energy and capacity for enjoyment lusty appetite for life. nervous suggests especially the forcibleness and sustained effectiveness resulting from mental vigor nervous energy.