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thickheaded; obtuse; stupid
slow; sluggish; inert; lethargic
indulgent (esp. to the opposite sex); doting
あいつは動きが鈍いなあ。
That guy's movements are so slow.
彼は反応が鈍いので何度も説明しなければならない。
His movements are slow and troublesome.
彼は何度説明しても理解できず、本当に鈍かった。
No matter how many times I explained, he couldn't understand — he was really obtuse.