mangrove jack noun2 •(Australia) An edible marine and estuarine fish, Lutjanus argentimaculatus, of northern Queensland.He turned and raised his hat, grinning and holding up a plastic bag in his other hand for her to see. ‘I brought some mangrove jacks for your lunch.’ — 2002 •(Australia, no longer used) The mangrove heron, Butorides striatus. formsmangrove jacks