Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ad-neptis (atn-), is, f., a daughter of the abnepos or of the abneptis, i. e. a granddaughter of a great-grandchild, i. e. a fourth granddaughter, antith. to the atavia, Dig. 38, 10, 1, § 7.