shudder
顫 centers on involuntary trembling or shivering, especially of the body or head, as in a shudder from cold, fear, or strong emotion.
顫 combines 亶 (likely contributing the sound) with 頁 (head), suggesting a trembling or shaking of the head. The exact historical development is uncertain.
The left side 亶 looks like a tall, unstable stack, and the right side 頁 is a head. Picture a head on top of a wobbly stack, shuddering and trembling as it tries to keep balance.
For セン, imagine a shudder so intense it sends a chill down your spine: send -> セン, as the cold sends shivers through your body.