To relieve congestion; to clear blockage or overcrowding from something, especially passages or areas.
From de- + congest (cause accumulation), from Latin congerere (heap together). Decongest literally means to reverse the heaping up of things.
Cold medicine labels say 'decongestant' because these drugs shrink swollen nasal tissues to open passages—your body's inflammation is literally blocking airflow like traffic on a highway.
Complete word intelligence in one call. Free tier — 50 lookups/day.