lymphocyte (n.)

in physiology, "colorless fluid found in animal bodies," 1725, from French lymphe (16c.), from Latin lympha "water, clear water, a goddess of water," variant of lumpæ "waters," altered by influence of Greek nymphē "goddess of a spring, nymph."

The same word was used earlier in English in the classical sense "pure water, water" (1620s) and with reference to colorless fluids in plants (1670s). Also see lymphatic. Lymph node is attested by 1874.