IPA: //ʌnˈsteɪtɪd//
KK: /ʌnˈsteɪtɪd/
Not clearly expressed or mentioned; something that is implied but not directly said.
The rules of the game included some unstated assumptions that players needed to understand.
Unstated → It is formed from "un-" (meaning not) and "stated" (from Latin "statuere", meaning to set or establish). The word "unstated" means not set forth or not established in words.
Think of 'not' ('un-') and 'set forth' ('stated') — that's why 'unstated' means something that hasn't been expressed.