Which term describes a process that is burdensome and requires significant effort?

The term that describes a process that is burdensome and requires significant effort is "onerous." This word specifically conveys the idea of something being not only challenging but also involving a heavy load or duty that is difficult to bear. When a task is considered onerous, it implies that it demands a considerable amount of work and can often lead to fatigue or frustration due to its demands.

In contrast, "effortless" refers to something requiring little to no effort, which directly opposes the notion of being burdensome. "Overbearing" can describe a domineering attitude or behavior, rather than the heaviness of a task. Lastly, "minuscule" denotes something very small or insignificant, which does not align with the idea of a substantial burden. Hence, the term "onerous" is the most fitting for describing a process that is both burdensome and demanding significant effort.