1. To abandon or leave behind one because someone assumes one is dead or is going to die. A noun or pronoun is used between "leave" and "for dead." The injuries were so severe that we had no choice but to leave the wounded soldiers for dead. The other members of his climbing expedition had left him for dead, but he survived the fall and managed to crawl his way back to camp.

2. To abandon or ignore something, such as a project, company, plan, etc., because it is expected to fail or is not important enough to succeed. A noun or pronoun is used between "leave" and "for dead." Often used in passive constructions. It is yet another business that has been left for dead by a government unwilling to subsidize the market for vulnerable companies. We tried our best to get into the smartphone racket, but after we failed to gain any real traction in the market, app developers left our new operating system for dead after just six months.