sticklebackPronunciation: /ˈstɪk(ə)lbak/Definition of stickleback noun a small fish with sharp spines along its back, able to live in both salt and fresh water and found in both Eurasia and North America. Family Gasterosteidae: several genera and species, including the common and widespread three-spined stickleback (Gasterosteus aculeatus) Origin: late Middle English: from Old English sticel 'thorn, sting' + bæc 'back'stickleback in other Oxford dictionaries Definition of stickleback in the US English dictionary