• Etymology Today from M-W: lethargic \luh-THAHR-jik or leh-THAHR-jik\
*1 : of, relating to, or characterized by drowsiness or sluggishness
2 : indifferent, apathetic

In Greek mythology, Lethe was the name of a river in the underworld that was also called "the River of Unmindfulness" or "the River of Forgetfulness." Legend held that when someone died, he or she was given a drink of water from the river Lethe to forget all about his or her past life. The name of the river and the word "lethargic" both derive from "lethe," Greek for "forgetfulness."

similarly sluggish:
stoic \STOH-ik\
1 capitalized : a member of a school of philosophy founded by Zeno of Citium about 300 B.C.
2 : one apparently or professedly indifferent to pleasure or pain

Zeno of Citium was a Syrian merchant who lost his fortune at sea. In Athens he was consoled by the Cynic philosopher Crates, who assured him that money didn't bring happiness, and he was so impressed that he founded his own school of philosophy and began teaching at a public hall called the Stoa Poikile. Zeno's philosophy, Stoicism, took its name from the hall where he taught, and it preached self-control, fortitude, and justice; passion was seen as the cause of all evil. By the 14th century, English speakers had adopted the word "stoic" as a general term for anyone who could face adversity calmly and without excess emotion.

• Previous E.T.