Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ectăsis, is (acc. -in), f., = ἔκτασις, the lengthening of a vowel short by nature: si brevis est per naturam, sed hoc loco ectasin fecit, Serv. Verg. A. 1, 343.