Uncertain, but possibly young child's pronunciation of thanks.
Alternatively, derived from Danish tak, from Old Norse þǫkk, from Proto-Germanic *þankō, *þankaz.
Go on, break out a "how's yew 'uns doin'? Right pleasure ta meet yew ’uns"! 2009, Kiyohiko Azuma, “The Osakan's here y'all”, in Stephen Paul, transl., edited by Yen Press, Azumanga Daioh Ominbus, New York City, →ISBN, page 29:
Altered from si in the 19th century to prevent having two notes of the musical scale starting with the same letter, to become ti. vowel changed to 'a' to signify a flattened note.
Meanings
(uncountable) In solfège, the lowered seventh note of a major scale (the note B-flat in the fixed-do system): te.