Which term describes a person who is habitually lazy or idle?

The term "sluggard" specifically refers to a person who is habitually lazy or idle, emphasizing a consistent lack of effort or motivation to engage in activities. It conveys a sense of sluggishness and an unwillingness to exert energy in tasks that require effort, which aligns perfectly with the definition of habitual laziness.

In contrast, the other terms hold different meanings: "staunch" describes someone who is loyal and committed, often in a strong or unwavering manner; "soporific" pertains to something that induces sleep or drowsiness, not laziness as a personality trait; and "serene" refers to a calm or peaceful state, which does not imply idleness or laziness. The distinct definition of "sluggard" makes it the most accurate choice for describing a person characterized by habitual laziness or idleness.