1. （潮水或海水）退，落
    When the tide or the sea ebbs, its level gradually falls.

    e.g. When the tide ebbs it's a rock pool inhabited by crustaceans.
           退潮时，它便成为甲壳动物居住的岩石区潮水潭。

2. 退潮（期）;落潮（期）
    The ebb or the ebb tide is one of the regular periods, usually two per day, when the sea gradually falls to a lower level as the tide moves away from the land.

    e.g. ...the spring ebb tide...
           春季退潮
    e.g. We decided to leave on the ebb at six o'clock next morning.
           我们决定第二天早晨6点钟趁退潮时离开。

3. 衰退;减退;减弱
    If someone's life, support, or feeling ebbs, it becomes weaker and gradually disappears.

    e.g. ...as a man's physical strength ebbs...
           随着人体力的衰退
    e.g. Were there occasions when enthusiasm ebbed?
           会有热情减退的时候么？

4. 处于低潮;处于衰退状态
    If someone or something is at a low ebb or at their lowest ebb, they are not being very successful or profitable.

    e.g. ...a time when everyone is tired and at a low ebb...
           每个人都疲惫不堪、处于低潮的一段时间
    e.g. The Government's popularity is at its lowest ebb.
           政府的支持率跌到了最低点。

5. 起伏;消长；盛衰
    You can use ebb and flow to describe the way that something repeatedly increases and decreases or rises and falls.

ebb的反义词

    e.g. ...the ebb and flow of feeling and moods.
           感觉和情绪的起伏