Which term indicates something that is not steady and is irregular instead?

The term "fitful" describes something that occurs in irregular or intermittent bursts, suggesting a lack of steadiness or consistency. For example, a fitful sleep pattern might involve waking frequently instead of sleeping soundly through the night. This aligns perfectly with the idea of something being irregular or not steady.

In contrast, "copious" refers to a large quantity or abundance, which does not imply anything about steadiness. "Prostrate" typically means lying flat or being in a state of extreme weakness or exhaustion, which is unrelated to the concept of irregularity. "Acrid" describes a sharp, bitter taste or smell, again having no connection to steadiness or irregularity. Therefore, "fitful" is the term that accurately captures the essence of something that is not steady.