You will almost only meet this word inside the fixed phrase 'on the warpath'. It means someone is angry and actively looking for the person who caused it, so they can shout at them or punish them. The picture is of somebody marching around the office or the house, face like thunder, hunting: 'The boss is on the warpath — she's found out about the missing files.' 'Dad's on the warpath about the broken window.' It is informal and half-joking, spoken between people who are watching from a safe distance, and there is usually a note of 'stay out of the way' in it. Two things to know honestly. First, the phrase almost never appears any other way — not 'a warpath', not 'the warpath' alone; learn the whole chunk, be on the warpath / go on the warpath. Second, where it comes from: it is from the wars of Native American peoples, and 'on the warpath' was English speakers' description of warriors setting out. Because of that origin, some people now feel uncomfortable using it, especially in North America. It is not a slur and it is still widely said, but it is worth knowing that background so the choice is yours.