入木三分的英文：
[Literal Meaning]
penetrate/wood/three/fen, one tenth of an inch
The ink has seeped into the wood three fen.

[解释]
形容书法极有笔力。现多比喻分析问题很深刻。

[Explanation]
with bitter incisiveness

[例子]
你对这篇文章的分析真是入木三分，我们都很佩服你的独到见解。

[Example]
Your analysis of the article was really profound and we all admire your insight.

[英文等价词]
written in a forceful hand
penetrating

Lao Wang's analysis was really penetrating.
老王的分析真是入木三分。