means Moving, reacting, or functioning slowly and without energy, as if reluctant to get going at all.

from From 'slug' — not the bullet but the slow, slimy garden creature — plus the adjective ending '-ish.' The word 'slug' for a sluggard or slow-moving person dates to Middle English, possibly of Scandinavian origin (compare Norwegian dialect 'slugg,' a heavy body). By the late 1400s, calling someone 'sluggish' tied them to that creeping, trail-leaving snail-cousin: a person who oozes through life at gastropod speed.