Lethean refers to something that induces forgetfulness or oblivion. There are a number of synonyms for Lethean depending on the context. For instance, there is amnesiac, which refers to a drug or substance that causes forgetfulness. Another synonym is soporific, which describes something that induces sleep and hence forgetfulness. Other words that can be used include narcotic, anodyne, and somniferous. These words are often used in literature and poetry to describe the effects of substances or events on the mind. Regardless of the word used, the idea of Lethean often carries with it a sense of loss and disconnection from the past.