'ta' originates from English, specifically a shortened/informal form of the phrase 'thank you', where 'thank' meant 'to express gratitude'.

'ta' changed from dialectal and child-language forms such as 'tah' or simple 'ta' used in regional British and Australian speech and eventually became the modern informal exclamation 'ta'.

Initially used as a child's or dialectal utterance (a short, informal token of gratitude), it has retained that basic sense and is now a common informal British English way to say 'thank you'.