Note the following quote from, "What Mormons Think of Christ" (LDS publication, pages 32-34):
"Christians speak often of the blood of Christ and its cleansing power. Much is believed and taught on this subject, however, it is utter nonsense and so palpably false that to believe it is to lose one's salvation."
Of the essential doctrines (that there is only one God, Jesus is God in flesh, forgiveness of sins is by grace alone, and Jesus rose from the dead physically, the gospel being the death, burial, and resurrection of Jesus), Mormonism denies three of them: how many gods there are, the person of Jesus, and His work of salvation.
There are dozens of possible definitions of "Christian," (that is, ways in which people use the word) even in addition to those in the dictionary, and they range all the way from very broad ("a Christian is anyone who tries to live his life by the teachings of Jesus") to very, very narrow ("a Christian is someone whose views and beliefs about Jesus Christ are exactly like mine").
In fact, the Mormons think that they (the Mormons) are the only "true Christians."
It is an ironic fact of Mormon history that when I was growing up Mormon in the 1940s, we Mormons were quite proud of the fact that we weren't "Christian," but rather "Mormon." At that time we Mormons understood that to be Christian was to subscribe to all the false doctrines of the Methodists, Lutherans, Catholics, and other false churches. It is only in the last few decades that the Mormon church has changed its attitude, and now wants desperately to be considered among the "Christian" churches, probably because they consider that by accepting the label "Christian" they will not appear so unusual in the eyes of unaware prospective converts, who only find out later that the Mormons have quite different definitions of "Christian," "God," and hundreds of other terms used by traditional denominations.
Mormonism is not Christian because it denies some of the essential doctrines of Christianity, including: 1) the deity of Christ, 2) salvation by grace, and 3) the bodily resurrection of Christ. Furthermore, Mormon doctrine contradicts the Christian teaching of monotheism and undermines the authority and reliability of the Bible.