Vigorous, a.
Etymology: [Cf. OF. vigoros, F. vigoureux, LL. vigorosus.]
1. Possessing vigor; full of physical or mental strength or active force; strong; lusty; robust; as, a vigorous youth; a vigorous plant. Famed for his valor, young, At sea successful, vigorous and strong. Waller.
2. Exhibiting strength, either of body or mind; powerful; strong; forcible; energetic; as, vigorous exertions; a vigorous prosecution of a war. The beginnings of confederacies have been always vigorous and successful. Davenant. -- Vig"or*ous*ly, adv. -- Vig"or*ous*ness, n.
Shades of meaning
Fernald has no entry of its own for vigorous; he lists it under active, healthy.
He lists it without comment; the entries above explain its neighbors.