The problem is that polytheism connotes the worship of many gods. Often these various gods represent objects or forces in nature, such as the Sun, the Moon, and so forth.
Perhaps the word you are looking for is tritheism, defined by my dictionary as "the doctrine that the Father, Son, and Holy Spirit are three distinct Gods." That more accurately describes our belief.
That said, I should point out that Mormons worship one God, God the Father, in the name of the Son (D&C 18:40; 20:29). So in that sense, we are monotheists.
Theologically, Mormons would have to come up with some doctrine more similar to the Trinity in order to be monotheists.
Even if we were to do as you suggest, it would not satisfy everyone's definition of monotheism. Muslims, who are strict monotheists, often call Trinitarian Christians "polytheists." To a certain extent, polytheism is in the eye of the beholder.
Thanks very much for your reply.
If I understand correctly, you are saying Mormonism does have three Gods, somewhat described as tritheism - three distinct Gods - however only one is worshiped, God the Father.
So, again if I understand you, there is a distinction drawn between having a God and worshiping a God.
I’m still not sure why tri (three) is not poly (more than one or many). The emphasis in Judeo-Christianity is strongly on monotheism, “Our God is One”, so clearly three would be verbotten.
This of course is why in orthodox Christian theology the Trinity is so central and important.
It is true that non-Christians, Muslims as you note, but also Jews, see the Trinity as insufficient monotheism; however, I would argue that Mormonism is at least one step further away. If one posits that the Trinity is insufficient monotheism, then Mormonism would have to be even more so.
I hope I’ve not misunderstood you and thanks again for your well-communicated and courteous reply.