松紧的英文：
degree of tightness; elasticity

参考例句：

Adjust the tension of a violin string,a tennis racket,etc
调小提琴弦、网球拍等的松紧

A device at the lower end of the bow for a stringed instrument, used for tightening the hairs.
松紧旋纽琴弓尾端的装置，用于松紧金属丝

In our childhood, we sewed an elastic band inside our trousers to serve like today's waistband.
小时候，我们的裤子都是不系腰带的， 就缝一根松紧带在里边。

Soon he returned in a shirt, slacks and sandals, and found her eating with appetite
不一会儿，他穿着衬衣，松紧裤和便鞋回来了，看到她吃得正香呢。

For a string of specified length, tautness and density only certain note can be generated
一根确定长度、松紧和密度的弦只能发出某某音。

Softly tailored waistcoats are fitted with and lined, with low armhole, front welts and an elastic back.
柔软西装式背心的特点是合身、有衬里、低袖窿、前身嵌线袋、后身装有松紧襻。

degree是什么意思：
n. 阶层；度；学位；程度

(degree of)importance,seriousness or influence
重要性、严重性或影响力（的程度）

current amplification degree
电流放大率

These universities are entitled to grant degrees.
这些大学有权授予学位。

tightness是什么意思：
n. 坚固，紧密；憋闷

tightness of warp
经纱紧密度

Stretch the rope tight, please.
请把绳子拉紧。

Uncomfortably tight and confining.
不适地紧绷的，不适地束缚的

elasticity是什么意思：
n. 弹性，弹力；灵活性，伸缩性

elastic resilience
弹性回能|弹能

Rubber is elastic.
橡皮是有弹性的。

This plan is fairly elastic.
这个计划有相当的灵活性。