Something, such as a drink or a drug, capable of making one forget suffering.
From Grecian ne- not, and penthos grief
First mentioned in Homer's Odyssey as a potion capable of erasing all bad memories. By extension, the use of nepenthe today largely reflects the reputed powers of alcohol to get rid of the memory of one's woes.
Though Bob usually enjoyed the rounds of funny emails circulating through his work address - the lolcats, the 'fail' pictures and motivationals especially - when he opened the email titled 'Next Time Your Girlfriend Says She's Ugly, Just Show Her THESE Ladies!' he soon found he'd need a strong nepenthe - and in large qualities - to unsee what had been seen.
*On pronunciation - sources suggest that it's supposed to be 'ni-pen'thee', but my classical studies teacher, a speaker of Greek, always called it 'neh-penth,' without the 'ee' sound at the end.