If someone or something is in extremis, they are in a very difficult situation and have to use extreme methods. [formal] ⇒ Yet now he was here, in extremis, to seek an alliance. ⇒ The use of antibiotics is permitted only in extremis.
2. phrase You can say that someone is in extremis when they are very ill and likely to die. [formal] ⇒ ...to treat patients who were in extremis.
COBUILD Advanced English Dictionary. Copyright © Harper Collins Publishers