For a long time, I've been using the word 'nickname' to mean an unofficial name given to a person. However, as time went by, it became evident to me that the English use of 'nickname' seems to imply (but I'm not sure if this is a rigid requirement) that an individual can arbitrarily choose, or, conversely, veto a nickname choice. Thus, it seems to be the case that in the English language, 'nickname' has a meaning closer to 'this is how I call myself unofficially' rather than 'this is how others call me unofficially'.
What words can I use when I need to convey specifically the latter meaning? What word can I use to convey specifically the former one - is 'nickname' strictly used in the former meaning? Finally, what word should I use when I want to encompass both concepts?