明锐的意思

sharp = on the ball = alert; aware Your expression is unusual. Unless he is referring to a real object used for killing people.

The point of a spear is very sharp, so " as sharp as a spear" means the object you are talking about is very sharp, pointed and dangerous. If you are referring to the intelligence of a person, the idiom is " as sharp as a tack"

Thank you for your information. I looked it up in every dictionary available but couldn't find it.

I have never heard this expression before, perhaps it is a regional thing. Where I live we often say 'He isn't the sharpest tool in the shed' which means He isn't very bright/smart. I hope someone can provide you with an answer, I would be interested in the meaning.