心血来潮 (xīn xuè lái cháo) — to be seized by a sudden whim; to act on a sudden impulse

A drawing of the thing itself, worn down over three thousand years into a few strokes.

The shape of 心 comes from a drawing of a heart, now highly stylized.

Two or more meaningful parts placed together so that their meanings combine into a new one.

The shape shows 一, a drop of blood, inside 皿, a container, for blood held in a sacrificial vessel.

A drawing of the thing itself, worn down over three thousand years into a few strokes.

This origin belongs to the traditional form 來; 来 is its simplified writing.

The traditional form 來 shows a wheat plant: a central ear, upward leaves, and downward stem and roots. The simplified 来 is a later shorthand.

Most characters — around four in five — are built this way: one part hints at the meaning, the other at the pronunciation.

潮 has 氵, the water form 水, on the left to show a water connection, with 朝 on the right giving the sound.