D defs.my
Entry 1 sense Webster, 1913

Irrotational

· Ir·ro·ta·tion·al · IPA
01 a. Not rotatory; passing from one point to another by a movement other than rotation; -- said of the movement of parts of a liquid or yielding mass.
  1. 1.
    Not rotatory; passing from one point to another by a movement other than rotation; -- said of the movement of parts of a liquid or yielding mass.(Physics)