Dull

暗淡

àndàn

(not shiny)

枯燥

kūzào

(boring, not exciting or interesting — see also boring)

沉悶 /沉闷

chénmèn

(not clear, muffled)

無聊 /无聊

wúliáo

(boring, not exciting or interesting — see also boring)

蠢

chǔn

(not bright or intelligent)

鈍 /钝

dùn

(lacking the ability to cut easily; not sharp)

陰沉 /阴沉

yīnchén

(cloudy, overcast)

软化

ruǎnhuà

(to soften, moderate or blunt)

钝化

dùnhuà

(to become dull)