“The one who has gone to suchness” or "The one who has arrived at suchness"
In this word one may find the words
tat and
gata.
The one gone to the state of the
Buddhas, free of all afflictions of karma and rebirth.
See also
wikipedia.
In Tibetan it is pronounced as Tayata, that word has also accumulated the following meaning: (it is/do it) like this.