*insession*

n. [ L. insessio, fr. insidere, insessum, to sit in. See Insidious. ] [ 1913 Webster ]

1. The act of sitting, as in a tub or bath. “Used by way of fomentation, insession, or bath.” [ R. ] Holland. [ 1913 Webster ]

2. That in which one sits, as a bathing tub. [ R. ] [ 1913 Webster ]

Insessions be bathing tubs half full. Holland. [ 1913 Webster ]