Zealous means full of eager enthusiasm for a cause. A zealous reformer, zealous in his duties, over-zealous.
It is admiring at moderate strength and worrying at full: over-zealous is the commonest form and it is always a criticism. Note zeal, zealot; and that zealous and jealous are the same Greek word arriving twice — zelos meant both zeal and jealousy, which is a striking pairing.
1adjectivezealousFull of eager enthusiasm for a cause.
“The zealous volunteers knocked on every door in town to collect signatures.”
synonyms: fervent, ardent
zealous is a quality of enthusiasm.
Latin zelosus comes from Greek zelos, zeal or jealousy. Jealous is the same word arriving through French.
Latin
zēlōsus
Middle English
zelose
English, today
zealous
Built from
From Middle English zelose, from Latin zēlōsus. From Middle English zelose, from Latin zēlōsus, from zēlus + -ōsus, from Ancient Greek ζῆλος (“zeal, jealousy”), from ζηλόω (“to emulate, to be jealous”). by surface analysis, zeal + -ous. a doublet of jealous.
Etymology from Wiktionary, CC BY-SA