"Veritas" is a Latin word meaning truth.
If you are looking for the Celtic equivalent of "truth," it would depend on which Celtic language you are interested in:
* Irish: Fírinne
* Scottish Gaelic: Fìrinn
* Welsh: Gwir
* Breton: Gwir
* Cornish: Gwir
These are all cognate words, meaning they share a common ancestor with the Latin "Veritas".