开颜的英文：
smile

参考例句：

Liu learned from Yan Zhenqing's calligraphy style, but his brush strokes were much thinner.
柳公权出于颜体，但避开颜字的肥壮，而变为瘦硬森挺

smile是什么意思：
v. 微笑，笑；惠及，露出（笑容）
n. 微笑；笑容

He smiled a discreet smile.
他的脸上露出带思虑的微笑。

a responsive smile
表示回答的微笑

What are you smiling at?
你笑什么?

A man may smile and smile and be villain
笑里藏奸

face melt in smiles; all smiles; beam with satisfaction
眉开眼笑