Vigor and vigour mean vitality, physical strength, energetic growth, validity. Vigor is the American spelling, vigour is the British spelling. Vigorous means robust, filled with energy, physically strong. Vigorous is an adjective, the adverb form is vigorously, the noun form is vigorousness. Note that the correct spelling in both American and British English is vigorous. Vigor appears around 1300 from the Anglo-French vigour, derived from the Latin vigorem meaning liveliness, activity, force. Vigorous appears around the same time from the Anglo-French vigrus, derived from the Latin vigere, meaning be lively, flourish, thrive.
Examples
With Cruz speaking to the assembled crowd in the background, Trump didn’t quite come out in support of Boehner’s removal as speaker to a group of reporters, but he did say he was disappointed in him and his “vigor”. (The Daily Caller)
“Not only does it provide access to this priceless collection, but it brings a new vigor to our arts education, and to the entire campus.” (The Washington Business Journal)
Perhaps influenced by the band’s relentless touring schedule and multiple festival appearances, the 10 tracks erupt with vim and vigour. (The Straits Times)
While our members believe some uncertainty is a price worth paying to resolve EU membership, delay puts a brake on decision-making, investment and the vigour of their businesses. (The Scotsman)
Indian cricket team goes through vigorous training ahead of South Africa series. (The Indian Express)
Vigorous community conversation needs to get underway regarding the future of high school education in Milpitas (The San Jose Mercury-News)
This scandal should begin a vigorous debate about the values that software developers incorporate in their software, not just in the automotive industry but in every industry. (The Chicago Tribune)