Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ădoptīvus, a, um, adj. [adopto], pertaining to adoption, made or acquired by adoption, adoptive: filius, an adopted son: P. Scipio, Fragm. ap. Gell. 5, 19 (opp. naturalis, a son by birth): filiorum neque naturalem Drusum neque adoptivum Germanicum patria caritate dilexit, Suet. Tib. 52: pater adoptivus, who has adopted one as son (or grandson, v. adoptio), an adoptive father, Dig. 45, 1, 107: frater, soror, etc., a brother, sister, etc., by adoption, not by birth, ib. 23, 2, 12, and 38, 8, 3; so also, familia, the family into which one has been received by adoption, ib. 37, 4, 3: adoptiva sacra, of the family into which one has been adopled (opp. paterna): neque amissis sacris paternis in haec adoptiva venisti, Cic. Dom. 13, 35: nomen, received by adoption (opp. nomen gentile), Suet. Ner. 41: nobilitas, nobility acquired by adoption, Ov. F. 4, 22.
Transf., of the ingrafting of plants (cf. adoptio): fissaque adoptivas accipit arbor opes, bears fruits not natural to it, ingrafted, Ov. Med. Fac. 5; Mart. 13, 46: quae sit adoptivis arbor onusta comis, Pall. de Insit. 20; cf. 144, 160 (cf. Verg. G. 2, 82: Miraturque (arbos) novas frondes et non sua poma).