buy
買 centers on the act of purchasing: exchanging money for goods. Its single core meaning is straightforward and concrete.
買 combines ⺫ (a net-like component) with 貝 (shell, an ancient currency), suggesting the idea of gathering shells to make a purchase.
Picture a net ⺫ draped over a pile of shells 貝, the old form of money. You gather shells in the net to go buy something.
For バイ, imagine you are at a market and you want to buy a bicycle: buy -> バイ. The sound of 'buy' is almost exactly the on'yomi, and you are buying with shells.
to buy; to purchase
buying; shopping
shopping; purchased goods
acquisition (esp. corporate); buy-out; takeover; purchase
trade; buying and selling; trafficking (e.g. of humans, arms, drugs); dealing
purchase; buying; buying out
procurement; purchase; buying
buying; purchasing; procurement
bargain; good buy; budget
buyer
going out to shop; going shopping
buying up of goods; cornering (market)
buying (in large quantities); (wholesale) purchase; buying in
repurchase; redemption
buying; purchasing; laying in
bargain; good buy
to buy up
restrained buying
speculatively buying a rice harvest, while the fields are still green
dollar purchase
brokerage; broker
to purchase; to buy in
buying power; purchasing power