Lewis & Short

ostĭātim, adv. [ostium].

  1. I. Lit., from door to door, from house to house (class.): ostiatim oppidum compilare, Cic. Verr. 2, 4, 24, § 53: agere crimen, to enumerate the several houses where a crime was perpetrated, id. ib. 2, 4, 22, § 48: nec scrutanda singula et velut ostiatim pulsanda, Quint. 5, 10, 112.
  2. II. Transf., by particulars or details (post-class.): quicumque ostiatim cupit noscere (wishes to know the particulars), legat, Vop. Carin. 17.