leave behind, gift
貽 centers on handing something over so it stays with someone else: leaving something behind or giving a gift. Both senses share the idea of transferring possession to another person.
貽 combines 貝 (shell, money, valuables) with 台, which likely contributes the sound. The character originally expressed giving valuables, hence the meanings of leaving behind or gifting.
The left side 貝 represents valuables like shells or money, and the right side 台 suggests a platform or stand. Picture placing a gift on a stand and leaving it behind for someone else to find.
For イ, imagine leaving behind an easel (イーゼル) with a gift on it: easel -> イ, and the gift stays behind.