Lymph, from the Latin lympha for "clear spring water". The Latin term can be traced back to the Greek Nymphe (with "L" replacing the "N" for reasons unknown). Nymphe were Greek goddesses of things pastoral, including pristine lakes and springs.

Greek anatomists such as Aristotle and Herophilus noted the existence of what are now called lymphatic vessels, but considered them simply as veins that carried water. Galen said these vessels didn't exist and, given his inexplicable power, such was the dogma for over 1400 years.

Spurred on with the discovery of lacteals by Gaspara Aselli in 1622, the lymphatic system was finally described by a number of anatomists during the mid to late 1600s. Thomas Bartholin, around 1660, was the first to use the term vasa lymphatic (lymphatic vessels), in reference to the watery fluid within (Bartholin's grandson, Kaspar, was the first to describe the greater vestibular glands of the female reproductive system, the erstwhile Barthonlin's glands).

In spite of the successes in illuminating its anatomy, it wasn't until the 1820s that the lymphatic system was understood not to be the general route of absorption, through the lacteals, of food and water.

Thomas Bartholin, 1616-1680 Public domain image