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Fëar (a Quenya word; sing. fëa; the Sindarin equivalent is fae) were the spirits or souls of incarnate creatures such as Elves and Men; they were one part of the makeup of these beings (the other part being the hröa, or body). Fëar were sent into Eä directly by Eru Ilúvatar; they are indestructible and are unable to dominated by any force within Eä, unless they give consent.
The word fëar is only used in reference to souls whose natural state is to be incarnated; those spirits that do not require a hröa in order to be complete are called ëalar ("beings").