adjective

1. mentally slow; stupid
2. lacking sensitivity; blunted in feeling or perception dull to grief
3. physically slow; slow-moving; sluggish
4. lacking spirit, zest, etc.; not lively; listless, insipid, etc.
5. not active or busy; slack a dull period for sales
6. causing boredom; tedious a dull party
7. not pointed or sharp; blunt; not keen a dull blade
8. not felt keenly; not acute a dull headache
9. 1. not vivid; not brilliant; dim a dull color
   2. not shiny or glossy; lusterless a dull finish
10. not distinct, resonant, etc.; muffled a dull thud
11. gloomy; cloudy dull weather

Etymology: ME dul < OE dol, stupid, akin to Ger toll < IE *dh(e)wel- < base *dheu-, blow, be turbid > dumb, dwell, OIr dall, blind, Gr thanatos, death

transitive verb, intransitive verb