"doctrine or belief that there is but one god," 1650s, from mono- "single, alone" + -theism "belief (of a specified kind) in God, a god, or gods."
Entries linking to monotheism
mono-
word-forming element of Greek origin meaning "one, single, alone; containing one (atom, etc.)," from Greek monos "single, alone," from PIE root *men- (4) "small, isolated."
-theism
word-forming element meaning "belief (of a specified kind) in God, a god, or gods," from Greek theos "god" (from PIE root *dhes-, forming words for religious concepts) + -ism.