一道 + (Adjective +) Noun
一道 (yīdào) combines the number 一 with the measure word 道 to mean "a beam of," "a streak of," or "a single." It is commonly used before nouns referring to light, cracks, or barriers. For example, 一道微弱的光 means "a faint ray of light."
窗帘缝里透进来一道阳光。
Chuānglián fèng lǐ tòu jìnlái yī dào yángguāng.
A ray of sunlight came through the gap in the curtains.
夜空中划过一道闪电。
Yèkōng zhōng huà guò yī dào shǎndiàn.
A bolt of lightning streaked across the night sky.
远处出现了一道美丽的彩虹。
Yuǎnchù chūxiàn le yī dào měilì de cǎihóng.
A beautiful rainbow appeared in the distance.