invigoration comes from invigorate (from in- 'into' plus Latin vigor 'liveliness', from vigere 'to thrive') plus the noun-forming suffix -ion. Morphologically, the ending is part of the etymology: the suffix is attached to the older base named in the history, producing a later English derivative. In present English, the noun sense is "the act of giving strength, energy, or fresh vitality", so the historical development ends in a clearly identifiable modern dictionary use. The same base also appears in related forms such as invigorate, vigor, and vigorous. Its semantic neighborhood includes revitalization, stimulation, energizing, and rejuvenation, which helps locate the modern sense without adding a separate etymological claim. The named historical forms include Latin vigor and Latin vigere.