Monism is the view that there is only one basic and fundamental reality, and that all existence is this one reality even though we discern different aspects of this reality. It is the idea that all that exists is of one substance.
“Monergism” is the teaching that God alone is the one who saves. It is opposed to “synergism” that teaches God and man work together in salvation. A good example is Cults are synergistic. Christianity is monergistic.
All sound very similar with quite different definitions.