Ye Olde English term to describe 'Ya Mum' it was regarded as a heavy insult back in the day and was even used in Shakespeare.
AN EXERPT FROM A SHAKESPEAREAN PLAY
A "Thee sir, are a dog."
B "Thy Mother is of my generation, what doth that make thee?"
by Gohn Gardenza November 4, 2007
The term "thy mother" is used to express jokes about your mom, in a Shakespearean way. It is generally used as a troll phrase.
Thangush engaged in suspicious activities with thy mother (new) last night
by iglooman69 June 30, 2022
a fancy way of saying the classic your mom joke.
guy: ah yes sir, thou art quite annoying.
other guy: FIE! thou mother/thy mother is incredibly ravishing.
by heart.stopped November 6, 2022