underestimate the real value or ability of; "Don't sell your students short--they are just shy and don't show off their knowledge"
sell securities or commodities or foreign currency that is not actually owned by the seller, who hopes to cover (buy back) the sold items at a lower price and thus to earn a profit
leave behind empty; move out of; "You must vacate your office by tonight"
leave (a job, post, or position) voluntarily; "She vacated the position when she got pregnant"; "The chairman resigned when he was found to have misappropriated funds"