rising tide; beginning
Literally the point where the tide begins to rise; also used figuratively for the start of something, often with a sense of momentum or opportunity. Somewhat literary or poetic.
When the tide starts to rise, it's time to go fishing.
His success began from a small start.
Compound of 潮 (tide) and 先 (tip, point, ahead). The exact historical derivation is uncertain, but the meaning is transparent from its components.