"Monotheism is not merely the cult of a single god, which would be called henotheism, but also implies the active rejection of all other gods. The recipient of monotheistic worship is not Heis Theos, “one god”, but Ho Monos Theos, “the only god”. Thus, Hindus worshipping an ishta devata, “chosen deity”, selected from among many, are henotheists but not monotheists. A Hindu who never worships any god except Shiva, but doesn’t object to his neighbour’s worshipping Krishna or Durga, fails the test of monotheism."
January 1, 1970
https://en.wikiquote.org/wiki/God_in_Hinduism