点睛之笔

1. • the brush stroke that dots in the eyes (idiom) fig. to add the vital finishing touch
2. • the crucial point that brings the subject to life
3. • a few words to clinch the point

Character by character

• 点(diǎn)point
• 睛(jīng)eye
• 之(zhī)(possessive particle, literary equivalent of 的 de)
• 笔(bǐ)writing brush