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slow-moving or inactive:

動きの鈍い, のろまな; 怠惰な, 無精な.

e.g. a sluggish stream.

lacking energy or alertness:

e.g. Alex woke late feeling tired and sluggish.

slow to respond or make progress:

e.g. the car had been sluggish all morning.

sluggishly | ˈsləɡiSHlē | adverb

sluggishness | ˈsləɡiSHnəs | noun

late Middle English: from the noun slug1 or the verb slug (see sluggard) + -ish1.