1725 in physiology sense, "colorless fluid found in the body," from French lymphe, from Latin lympha "water, clear water, a goddess of water," variant of lumpæ "waters," altered by influence of Greek nymphe "goddess of a spring, nymph." The word was used earlier in English in the classical sense "pure water, water" (1620s), also (1670s) with reference to colorless fluids in plants. Also see lymphatic. Lymph node is attested from 1892.
A clear, watery, sometimes faintly yellowish fluid derived from body tissues that contains white blood cells and circulates throughout the lymphatic system, returning to the venous bloodstream through the thoracic duct. Lymph acts to remove bacteria and certain proteins from the tissues, transport fat from the small intestine, and supply mature lymphocytes to the blood.