Lewis & Short

ălĭēnĭtas, ātis, f. [alienus]. In medic. lang.,

  1. I. The causes or materials of disease in the human system, which are extraneous to it: auferre alienitatem, Cael. Aur. Tard. 5, 4: alienitatis obtrusio, id. ib. 5, 64: manens alienitas, id. Acut. 3, 20.
  2. II. For alienatio (q. v. B.): mentis, Cael. Aur. Acut. 2, 39.