Lewis & Short

incrēdundus (incrēdendus), a, um, adj. [2. in-credo], not to be believed, incredible (Appuleian): fabula, App. M. 2, p. 120, 15: potentiae caerimoniarum, id. Flor. 2, p. 351: illecebrae frugum, id. Mag. p. 304, 25.