1 inactive, unreactive, unresponsive, neutral:
Argon, xenon, and neon are inert gases.
2 motionless, immobile, inanimate, lifeless, still, quiet, quiescent, stationary, static:
He was mute and inert: it was like talking to a zombie.
3 sluggish, slow, torpid, dull, inactive, idle, indolent, lazy, slothful, leaden, slack, passive, supine, dormant, otiose, listless, languid or languorous:
I contemplated the inert bodies sunbathing around the swimming-pool.