買空賣空

to speculate / to play the market / (fig.) to sell hot air / to swindle people by posing as a reputable operator

to buy / to purchase

to buy on margin (finance)

empty / air / sky / in vain

to empty / vacant / unoccupied / space / leisure / free time

to sell / to betray / to spare no effort / to show off or flaunt

to sell short (finance)