Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
exstăsis (ext-), acc. in; abl. i, f., = ἔκστασις, terror, amazement, Vulg. Act. 3, 10 (= stupor, id. Luc. 5, 26); cf. id. Psa. 30, tit.