the word vigorous originates from the latin adjective 'vigorosus', meaning 'full of vigor'. this, in turn, derives from the latin noun 'vigor' (active strength, liveliness), which is built upon the verb 'vigere' (to be lively, to thrive). the underlying proto-indo-european root is believed to be weg- meaning 'to be strong, lively', which also gives rise to english words like 'wake' and 'watch'. thus, the literal sense of 'full of liveliness' evolved seamlessly into the modern meanings describing energetic activity or robust physical growth.

Structure: vigor (active strength) + ous (adjective suffix) vigor (from latin 'vigor', meaning 'liveliness, activity', from the verb 'vigere', 'to be lively, to thrive'); ous (a suffix forming adjectives, from latin '-osus', meaning 'full of, characterized by')