1
- the fourth letter of the Greek alphabet (Δ, δ), transliterated as 'd'.希腊字母表中第四个字母（译写为d）。
1.1
- Brit. a fourth-class mark given for an essay, examination paper, or other piece of work〈英〉（论文、考试成绩等的）δ等, 丁等。
1.2
- as modifier the fourth in a series of items, categories, etc.丁, δ项, δ类 （一系列项目、分类中的第四位） ：
delta hepatitis.
丁型肝炎。
1.3
- (Delta)followed by Latin genitive Astronomy the fourth (usually fourth-brightest) star in a constellation【天文】δ星（星座中第四颗星, 通常亮度也居第四位） ：
Delta Cephei.
仙王座δ星。
2
- a code word representing the letter D, used in radio communication（无线电通讯中字母D的代码词）Δ,δ.
1.1
- (δ) Mathematics variation of a variable or function【数】变量。
1.2
- (Δ) Mathematics a finite increment【数】有限增量。
1.3
- (δ) Astronomy declination【天文】偏差。
词源
Greek， from Phoenician daleth.