series

(philosophy, Gnosticism) aeon

taboo

Belgrade (the capital city of Serbia)

(mineralogy) opal, a mineral consisting, like quartz, of silica, but inferior to quartz in hardness and specific gravity

diesel

member, a person who is in a group / participant, attendee at an event / (programming) member in object-oriented programming / (Internet slang) suspect in a crime

Madrid (a city and municipality of the Community of Madrid, Spain; capital city of Spain) / Madrid, Community of Madrid (an autonomous community of Spain)

(music) fugue

(fiction, Internet) troll