Definition of "incompressible"

incompressible

adjective
not comparable
1. Not compressible.
  Quotations
  As water [trapped in the cylinders] is incompressible, a momentary leap in [steam] pressure is liable to occur in starting; […] .
  1951 March, Cecil J. Allen, “British Locomotive Practice and Performance”, in Railway Magazine, page 188
2. (calculus, of a vector field) Having a divergence equal to zero.