ebb /eb/ 在古英语时期就有"退潮"的意思，名词和动词两种词性。

We decided to leave on the ebb at six the next morning.

我们决定在第二天早上6点趁退潮时离开。(n.)

When the tide ebbs, you can paddle out for a mile and barely get your ankles wet.

退潮时，你可以蹚着水走出一英里远而几乎湿不到脚踝。(v.)

到了14世纪，ebb 又有了引申义：衰退，减退，常与 away 搭配。

The pain was ebbing.

疼痛逐渐减轻了。

As the night fell, our enthusiasm began to ebb away.

随着夜幕降临，我们的热情渐渐低落。

That was a time when everyone was tired and at a low ebb.

那是一个大家都处于疲惫和低潮的时期。

ebb 的反义词为 flow， ebb and flow 用来比喻事物的盛衰，消长，起伏。

the ebb and flow of the seasons：四季更迭 (n.)

Life's complicated. Emotions ebb and flow.

人生很复杂，感情起伏不定。(v.)

ebb 的近义词：

说完地上的 ebb，就不得不提天上的wane /weɪn/。

wane 也是两种词性和两层含义，一指月亮的亏缺：

The moon is waning and rises later every day.

月亮渐亏，每天出现的时间也越来越晚。

另一个指减弱和衰败：

Her enthusiasm for the whole idea was waning rapidly.

她对整个想法的热情迅速冷淡下来。

Her popularity has been on the wane over the years.

这几年她的人气江河日下。

wane 与其反义词搭配：wax and wane，也类似 ebb and flow 的含义，指盈亏，兴衰，成败。

* 其它相关表达：潮起潮落

As the moon waxes and wanes, the height of the tide changes.

随着月亮的盈亏，潮汐高度也发生着变化。

As they spoke, his attention seems to wax and wane.

他们说话时，他的注意力时而在线，时而掉线。

电影里的 ebb：

图片截自2018年第90届奥斯卡最佳影片 《三块广告牌》(Three Billboards Outside Ebbing, Missouri)，片名中的 Ebbing 并非今天聊的 ebb，而是影片中位于密苏里州的虚构地名。

名著中的 ebb：

He blew his nose on a corner of the filthy pillowcase he wore, looking so pathetic that Harry felt his anger ebb away in spite of himself.

- Harry Potter and the Chamber of Secrets by J.K. Rowling

他用他的鼻子朝他身上那脏兮兮哦枕套一角吹了吹气。他看起来那么可怜，以致于哈利觉得他的怒气一下全消失了。

- J.K.罗琳《哈利·波特与密室》

They looked out across the endless acres of Gerald O'Hara's newly plowed cotton fields toward the red horizon. Now that the sun was setting in a welter of crimson behind the hills across the Flint River, the warmth of the April day was ebbing into a faint but balmy chill.

- Gone with the Wind by Margaret Mitchell

他们都朝着杰拉德·奥哈拉那片延伸到天边的新开垦棉田望去，一直望到那红彤彤的地平线。太阳落在弗林特河那边的群山后，映得一片深红，暖洋洋的四月天渐渐有点儿淡淡的凉意了。

- 玛格丽特·米切尔《飘》