枯燥
kū zào · HSK 7
uninteresting
🍂 枯 withered + 燥 parched = doubly dry, so dry it bores: dry-as-dust
Both characters mean dry: 枯 is a withered, dried-up plant and 燥 carries the fire radical 火 for parched heat. Stack two kinds of dryness and you get something so arid it is dull and uninteresting.