ears without rim
耼 centers on ears that lack a distinct outer rim or helix, describing a specific physical ear shape. The meaning is narrow and anatomical.
耼 combines 耳 (ear) with 冄, which likely contributes a phonetic element. The character is rare and its exact historical development is uncertain.
The left side is an ear 耳. The right side 冄 looks like a simplified ear shape without the outer rim. Picture an ear missing its outer curl, leaving only the inner structure.
For タン, imagine a tan-colored ear without a rim, like a smooth, sun-tanned ear: tan -> タン.