Choose the word that is most similar in meaning to the given word.

Sluggish

The correct option is Lethargic.

Explanation:
The given word is Sluggish, which describes someone or something that is slow-moving, lacking energy, inactive, or slow to respond.

Let's analyze the meanings of all the given options:
- Vigorous: Strong, healthy, and full of energy (Opposite in meaning).
- Lethargic: Affected by lethargy; slow, sleepy, and lacking energy (Most similar in meaning).
- Lively: Full of life, energy, or enthusiasm (Opposite in meaning).
- Energetic: Showing or possessing high levels of vitality or activity (Opposite in meaning).

Therefore, the word that is most similar in meaning to Sluggish is Lethargic.