passerine /ˈpæsəɹaɪn/adjective 2noun 1forms 1 adjective2 •Of or relating to the Passeriformes order of perching birds, which are generally anisodactyl, having three toes pointing forward and one back, which facilitates perching. •(no longer used) approximately the size of a sparrow. noun1 •Any bird of the order Passeriformes, which comprises more than half of all bird species. formspasserines