1. English and Irish  short form of or pet name for Thaddeus, a biblical name of obscure origin, probably from Greek, meaning possibly "gift of/given by God". Thady is an alternative Irish pet name.

2. In Ireland, Tadhg, from Gaelic "poet, philosopher" may also be Anglicized as Tad.

3. Tad may also be a given name in its own right in the US.