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. 2018
Examples from the Web for theirself
“We live in a society where there are girls who are in love with theirself and flaunt it but the majority are insecure,” says one.Cara Delevingne Posts Protest Picture Of Her Boob (With Taped-Out Nipple)
July 14, 2014
Word Origin and History for theirself
c.1300, variant of themself, with self, originally an inflected adjective, treated as a noun with a meaning "person." Related: Theirselves.
Online Etymology Dictionary, © 2010 Douglas Harper