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.
A person that looks at themself hella long in the mirror may be selfsexual.
by fcsuper May 4, 2006
the singular form of the plural noun.
my computer changes "themself" to "themselves" all the time.
by cheryl lemons April 2, 2008
A mythical pronoun occasionally sighted awkwardly straddling the thorny bush dividing plural from singular.

See myselves, mangluage.
"anybody who actually says this should kill themself."
by _m374 May 11, 2006
can be used to refer to a singular person if you don't know their gender.
That person refuses to run the marathon by themself.
by megamangohan August 9, 2020
A person is so fat they look like they have eaten themselves and there is 2 of that person, one person inside and one person outside.
That person is so fat it looks like they have eaten themself
by Rafphillips June 7, 2014