Pareus' four senses of immortality: unfallen Adam's was the power of not dying, given union with a perfect soul
Pareus likewise says that the immortality by which man before sin was immortal in body was a power of not dying, that is, the absence of the act of dying, on the supposition of its union with a soul perfect from its origin, although man's body was mortal in itself.
"Immortality," he says, "means first an inability to die that is absolute and by nature. In this sense God alone has immortality, and in this sense the Fathers deny, and we deny, that man was immortal by nature. Second, an inability to die by the grace of creation: so angels and human souls are immortal. Third, an inability to die by the grace of a gift: so the bodies of the blessed will have immortality. Fourth, a power of not dying, that is, the absence of the act of dying, on some supposition, though the thing is mortal in itself. In this sense man before sin was immortal in body, on the supposition of its union with an immortal soul perfect from its origin." (Pareus, against Bellarmine, On the Grace of the First Man, chapter 9.)
Latin
XXI. Et similiter Pareus immortalitatem illam, qua homo ante peccatum corpore immortalis erat, dicit fuisse potentiam non moriendi, seu negationem actus moriendi, ex hypothesi unionis cum anima originaliter perfecta, licet corpus hominis esset in se mortale. Immortalitas, inquit, significat primo impotentiam moriendi absolutam & natura. Sic solus Deus immortalitatem habet. Sic Patres negant, & nos negamus hominem immortalem fuisse natura. Secundo impotentiam moriendi ex gratia creationis: Sic Angeli, animae humanae sunt immortales. Tertio impotentiam moriendi ex gratia doni: sic corpora beatorum immortalitatem habebunt. Quarto potentiam non moriendi, seu negationem actus moriendi, ex aliqua hypothesi, licet in se sit mortale. Sic homo ante peccatum immortalis erat corpore, ex hypothesi unionis cum anima originaliter perfecta, immortali. In lib. adversus Bell. de Grat. primi hominis, cap. 9.