🔼The name Thummim in the Bible
The Thummim is one of two enigmatic items that were placed in the breastplate of the high priest; the other one being the Urim (Exodus 28:30).
We don't know what they were or what they were made of but the Urim and the Thummim were somehow used to consult God (Numbers 27:21, 1 Samuel 28:6). And whatever they were, the Urim and Thummim apparently survived until after the return (Nehemiah 7:65, here spelled תומים).
🔼Etymology of the name Thummim
The word thummim is most likely a derivation of the wonderful Hebrew root תמם (tamam), meaning to be complete:
The word thummim looks a lot like תמים (tamim), meaning complete, a word that is used to describe sacrifices — without blemish and perfect. Speech that is tamim is 'complete, entirely in accord with truth and fact,' as BDB Theological Dictionary has it. But the word thummim is a noun and thus probably a plural of either תם (tom), meaning integrity, or תם (tam) , meaning perfect.
Thummim means Perfections or Integrities.