Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ūnĭ-gĕnĭtus, a, um, adj. [unus-gigno], onlybegotten, only (eccl. Lat.; cf. unicus): unigenitus ille vocatur, qui parentibus solus sit, Hier. adv. Helv. 9: filius, Tert. adv Gnost. 7; Aug. Civ. Dei, 11, 24; Vulg. Johan 1, 14.