No, it is not "a monopoly", but it most certainly
can be abuse of monopoly power, depending on the circumstances.
Abuse of Monopoly Power | Economics Help
For example, in a market with high barriers to entry, a monopoly has the power to use predatory pricing to force smaller competitors out of business. Once they're out, it can then raise its prices to recoup losses and make plenty of profits on top. Because barriers to entry are high in this hypothetical market, it is long until - if ever - someone tries to reenter it to compete. And if we do not enforce anti-trust laws to stop that behavior, then nobody will reenter because the monopoly will always be able to temporarily drop prices low enough to drive them out of business.
This may not be the case with Amazon, but Nilly is not entirely wrong about the general proposition that monopolies can and have knock smaller competitors out with artificially lower prices.