Ebb (verb)

1. To recede or fall away, as the tide.
2. To decline or fade away gradually.

Origin:

From the old english word "æfnan" meaning "to recede".

Examples:

1. The tide began to ebb as the sun set.
2. The energy of the crowd began to ebb as the night went on.
3. The enthusiasm for the project began to ebb as the difficulties became apparent.
4. The ebb and flow of the tide is a natural phenomenon.
5. The ebb and flow of the stock market is hard to predict.