Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Prorsa (Prōsa), ae, f. [2. prorsus], sc. dea, i. e. the goddess presiding over births with the head foremost (opp. Postverta), Varr. ap. Gell. 16, 16, 4; cf. Hartung, Relig. d. Röm. 2, p. 199.