Is it the same meaning in tyrannosaurus as in thesaurus?
I really can’t imagine what those two words could possibly have in common!
The two etymologies are different.
In thesaurus, the -saurus isn’t a suffix. It’s part of the word. The word actually comes from the Greek word thēsaurós, which means treasure or treasury.
In tyrannosaurus, the origin is from the Greek words turannos, which means tyrant, plus the word sauros, which means lizard.
They have different origins:
So, obviously, they do not have the same meanings. Although some people do like to make jokes about this. Cf. What's a big vocabulary word for someone with a big vocabulary?
According to Wikipedia, thesaurus derived from Latin and meant “treasure store”. So assuming the first half of the word is treasure, then saurus must mean store presumably.
Contrarily, tyrannosaurus derived from the roots tyrannos and sauros from Greek, which meant “tyrant lizard”.
Therefore, since one derives from Latin and the other from Greek, I would assume the similarities in the roots are purely coincidental.