Douglas Harper's Etymology Dictionary
word-forming element meaning "god, gods, God," from comb. form of Greek theos "god," from PIE root *dhes-, root of words applied to various religious concepts, such as Latin feriae "holidays," festus "festive," fanum "temple."
pre. (context: religion) god or deity
Usage examples of "theo-".
The Monkey, surprisingly, gravitated to Theo- He showed no sign of resentment at Theo's new rank.