Zealous, a.
Etymology: [LL. zelosus. See Zeal.]
1. Filled with, or characterized by, zeal; warmly engaged, or ardent, in behalf of an object. He may be zealous in the salvation of souls. Law.
2. Filled with religious zeal. [Obs.] Shak. -- Zeal"ous*ly, adv. -- Zeal"ous*ness, n.
Shades of meaning
Fernald has no entry of its own for zealous; he lists it under eager.
He lists it without comment; the entries above explain its neighbors.