Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
prīvignus, i, m., and prīvigna, ae, f. [for privigenus, from privus-gigno; prop. of a separate race]. 
- I.  A step-son; a step-daughter (class.): uxor liberis ex aliā uxore natis noverca dicitur: matris vir ex alio viro natis vitricus appellatur: eorum uterque natos aliunde privignos privignasque vocant, Dig. 38, 10, 4. 
 
- A.  Privignus, Sall. C. 15, 2; Cic. Clu. 66, 188; id. Q. Fr. 3, 3, 2; Hor. Ep. 1, 3, 2; Prop. 2, 1, 52; Dig. 38, 10, 7: PRIVIGNVS MEVS, Monum. Ancyr.: venenum privigno datum, Juv. 6, 134.
 
- B.  Privigna: de uxore Tuberonis et privignā, Cic. Att. 13, 20, 2; Just. 14, 6, 3.
 
- C.  Plur.: illic matre carentibus Privignis mulier temperat innocens, step-children, Hor. C. 3, 24, 18; Dig. 23, 2, 34.
 
- II.  Transf., of plants (poet.), adj.: privignae proles, Col. 10, 161.