divination
彖 centers on divination, specifically the act of interpreting signs or casting lots to gain insight.
The exact historical development of 彖 is uncertain. It may have originally depicted a pig or animal used in divination rituals, but this is speculative.
The top 彑 looks like a pig's head, and the bottom 豕 is a pig. Imagine an ancient diviner reading the future from the entrails of a sacrificial pig.
For タン, picture a tan-colored pig being used in a divination ritual: tan -> タン, and the pig's entrails reveal the future.