Jealous is the sour feeling when someone else has what you want. Your friend's new flat, a colleague's promotion, the sibling who got the bigger slice: you look, and something turns over in your chest.
There is a second jealous, and it is the stronger one, about fearing that someone you love will be taken by a rival. That is the jealous husband, the jealous glance across a restaurant. It nearly always takes OF, as in jealous of her sister, jealous of his success, never jealous from or jealous about. Careful writers keep envious for the first sense and jealous for the second, while everyday English uses jealous for both, and I'm so jealous is a warm, ordinary reply to good news. There is a third use worth knowing: jealous of your privacy, jealous of its independence, meaning fiercely protective of something you already have. The noun is jealousy, and the possessive kind is what Shakespeare called the green-eyed monster.
1adjectivejealousUnhappy because someone else has something you want.
“He was jealous of his brother's easy way with strangers.”
2adjectiveafraidAfraid of losing someone's love or attention to a rival.
“She got jealous whenever he mentioned his ex.”
3adjectivefiercelyFiercely protective of something you have and will not share.
“He was jealous of his privacy and gave no interviews.”
Too few real examples of this word to estimate which sense is commonest.
Also accepted in games: envious
Jealous and zealous are the same word. Both go back to Ancient Greek zelos, which meant zeal, a burning eagerness, and jealousy at the same time. It came through Latin zelosus and Old French jalous into English around 1382, and the split happened later: one branch keeps the heat pointed at a cause, the other at a person.
Ancient Greek
ζῆλος — zeal, jealousy
Latin
zelosus
Old French
jalous
Middle English
jelous
English, today
jealous
1382. From Middle English jelous, gelous, gelus, from Old French jalous, from Latin zelosus, from Ancient Greek ζῆλος (“zeal, jealousy”). a doublet of zealous.
Etymology from Wiktionary, CC BY-SA