Themself

[Dianne]

Used instead of ‘himself’ or ‘herself’ to refer to a person of unspecified sex.

[Oralee]

[pron].
[Single] form of word themselves, used when refering to person whose sex (male or female) is not known or identified. Often used where the word them is used as [a single] form as well.

[Michiko]

the [singular] [form] of the [plural] noun.

[Luis Fok]

A mythical pronoun occasionally sighted awkwardly straddling the [thorny] bush dividing plural from singular.
See [myselves], [mangluage].