specialized, concentrated
耑 centers on the idea of something being focused or narrowed to a specific point: specialized or concentrated. It suggests a sharp, pointed direction of effort or attention.
The origin of 耑 is uncertain. It visually combines 山 (mountain) and 而, but the historical development is not clearly established.
Picture a mountain 山 that narrows to a sharp peak, with the lower part 而 suggesting a focused, concentrated point. The whole shape evokes something specialized and concentrated.
For タン, imagine a concentrated drop of tan-colored liquid falling from the mountain peak: tan -> タン, and the drop is specialized and pure.