Webster’s Revised Unabridged Dictionary · 1913
Isopycnic
I′so·pyc′nic (ī′sō·pĭk′nĭk), a. [Iso- + Gr. πυκνός dense.] (Physics) Having equal density, as different regions of a medium; passing through points at which the density is equal; as, an isopycnic line or surface.
I′so·pyc′nic, n. (Physics) A line or surface passing through those points in a medium, at which the density is the same.