dull

1 dull /ˈdʌl/ adjective
duller; dullest
1 dull
/ˈdʌl/
adjective
duller; dullest
Britannica Dictionary definition of DULL
1 
: not exciting or interesting : boring
2 
: having an edge or point that is not sharp
3 
of a sound : not clear and loud
4 
of pain : constant but not sharp or severe
5 
: not shiny
6 
: not sunny : having a lot of clouds
7 
: slightly grayish or dark : not bright
8 
old-fashioned : stupid or slow in understanding something
9 
: not having a lot of business or financial activity

(as) dull as dishwater

— see dishwater

(as) dull as ditchwater

— see ditchwater

— dullness

noun [noncount]

— dully

adverb
2 dull /ˈdʌl/ verb
dulls; dulled; dulling
2 dull
/ˈdʌl/
verb
dulls; dulled; dulling
Britannica Dictionary definition of DULL
: to become dull or to make (something) dull: such as
a  : to become or cause (something) to become less clear, distinct, bright, or shiny
[+ object]
[no object]
b  [+ object] : to make (something, such as a feeling) less sharp, strong, or severe
c  : to become or cause (something, such as a knife or blade) to become less sharp
[+ object]
[no object]