theirself

[ th air-self ]
/ ˌðɛərˈsɛlf /
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pronoun Nonstandard.

Also their·selves [th air-selvz] /ˌðɛərˈsɛlvz/.

Origin of theirself

1250–1300; Middle English; formed on analogy of myself
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for theirself