Lewis & Short

nătātĭo, ōnis, f. [nato], a swimming.

  1. I. Lit.: habeant igitur sibi arma, sibi equos … sibi pilam, sibi natationes atque cursus. * Cic. Sen. 16, 58: frigidae natationes, Cels. 3, 24 fin.
  2. II. Transf., a place for swimming, swimming-place, Cels. 3, 27, 1; Cael. Aur. Tard. 1, 1.