水すい泡ほう

noun

foam; bubbles

Literal meaning: foam or bubbles on the surface of water. Used in descriptive or scientific contexts.

• 川かわの流ながれに水すい泡ほうが浮うかんでいた。

  Foam was floating on the river current.

noun

coming to nothing; ending in failure

Idiomatic use, almost always in the set phrase 水泡に帰する (come to nothing, end in vain). The image is of plans or efforts vanishing like bubbles.