The word 'valiantly' is built on the core adjective 'valiant', which entered English from Old French in the 14th century. Its ultimate source is the Latin verb 'valere', meaning 'to be strong, to be of worth', a concept deeply connected to health, power, and moral fortitude. The adverbial suffix '-ly', of Germanic origin, was attached to transform the quality of bravery into the manner of performing an action. Thus, to act 'valiantly' is to conduct oneself with the strength and courage inherent in the ancient idea of 'valere'.

Structure: valiant (brave) + ly (adverb suffix) - 'valiant': From Old French 'vaillant', meaning 'brave, strong, worthy', ultimately from Latin 'valere' (to be strong, be well). - 'ly': A native English suffix forming adverbs from adjectives, from Old English '-lice'.