\In*ses"sion\, n. [L. insessio, fr. insidere,
insessum, to sit in. See {Insidious}.]
1. The act of sitting, as in a tub or bath. ``Used by way of
   fomentation, insession, or bath.'' [R.] --Holland.
2. That in which one sits, as a bathing tub. [R.]
         Insessions be bathing tubs half full. --Holland.