Thayan phrases are those with specific meaning in Thay. There are a number of these in common usage.
Fireball – (verb) to grow or become larger, greater, more intense, at an accelerating rate.
Kobold King – (noun) something silly and pointless, saying that something is nothing ;
Red Ring – (adj) used to indicate something manipulated, arranged, or otherwise set up or controled by a Red Wizard.
Scry – (verb) "I have it on good authority", typically gained by divination magic
Underbug – (noun) a person who is expected to lose in a contest or conflict.