Jealous  adj. 1 resentful of rivalry in love. 2 (often foll. By of) envious (of a person etc.). 3 (often foll. By of) fiercely protective (of rights etc.). 4 (of god) intolerant of disloyalty. 5 (of inquiry, supervision, etc.) Vigilant.  jealously adv. [medieval latin zelosus: related to *zeal]