The etymological origins of the word undómë are not completely obvious, except that -dómë means 'twilight' (with a connection to lómë, 'night'). The equivalent term for morning twilight was tindómë, which was explicitly 'starry twilight', but the meaning of un- in undómë is not so directly explained. It perhaps relates to a word for 'down' (presumably relating to sunset in this context), but that interpretation is far from certain.