expression, i-adjective
dim-witted; slow; simple-minded
A colloquial, mildly derogatory expression for someone who is not intelligent or slow to understand. Often used in casual speech.
彼は頭の弱い人だから、難しい話はしないほうがいい。
He's a bit slow, so it's better not to talk about complicated things.
あの子は頭が弱いわけじゃない。ただ勉強が嫌いなだけだ。
That kid isn't dim-witted; he just hates studying.