much, abundant, kind, considerate
腆 centers on generous abundance: having much, being plentiful, and showing kindness or consideration as a natural expression of that fullness.
腆 combines ⺼ (flesh) with 典, which likely contributes the sound and may suggest a sense of fullness or abundance. The exact historical development is uncertain.
The flesh radical ⺼ suggests a body, and 典 looks like a full, abundant container. Picture a person whose body is so well-fed and full that they overflow with kindness and consideration.
For テン, imagine a generous person giving you ten gifts: ten -> テン, and their abundant kindness fills the room.