A place, situation, or thing that is very boring and uninteresting; a state of extreme dullness.
From 'dull' + '-sville' (a suffix added to place names meaning 'place of'). This is primarily 1950s-60s slang, where '-ville' became a casual way to name hypothetical towns.
This is peak 1950s teen slang—Jack Kerouac and the Beats used 'Dullsville' to mean anywhere boring, making it the opposite of their sought-after 'cool' cities and experiences.
Complete word intelligence in one call. Free tier — 50 lookups/day.