Acting against sleep or preventing the effects of hypnotic (sleep-inducing) drugs.
From anti- (against) + hypnotic (sleep-inducing, from Hypnos, Greek god of sleep). An antihypnotic substance would counteract sedation or drowsiness.
Caffeine is a classic antihypnotic—it's why coffee stops you from falling asleep by blocking the very chemicals in your brain that make you tired.
Complete word intelligence in one call. Free tier — 50 lookups/day.