The antonyms of the word "most work-saving" are "labor-intensive," "time-consuming," "inefficient," and "onerous." "Labor-intensive" refers to a process that requires a lot of manual work and effort, whereas "time-consuming" refers to an activity that takes a long time to achieve. "Inefficient" means that something is not producing the desired outcome with minimal effort or resources. Lastly, "onerous" refers to a task that is challenging, unpleasant, or burdensome to perform. These antonyms of "most work-saving" indicate the opposite meaning where a lot of effort, time, and resources are needed to carry out a specific task or activity.