throw away
捐 centers on discarding or giving something up: throwing away, abandoning, or relinquishing.
捐 combines 扌 (hand) with 肙, which likely contributes the sound and may relate to discarding or giving away by hand. The exact historical development of 肙 is uncertain.
The hand radical 扌 beside 肙 suggests a hand throwing something away. Picture a hand tossing aside a small object represented by 肙.
For エン, imagine throwing away an envelope: envelope -> エン, and your hand discards it.