Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† ătypus, um, adj., = ἄτυπος, ον, that stammers in speaking, stammering: balbus autem et atypus vitiosi magis quam morbosi sunt, Cael. Sabin. ap. Gell. 4, 2, 5; so Dig. 21, 1, 10.