An omnishambles is a mess in every direction at once — not one broken thing, but the whole scene falling apart, usually because someone cannot do their job. It is a noun, British, and informal. People use it most about government: a plan that fails, then the excuse fails, then the next fix fails. The word is quite new. A British political comedy, The Thick of It, made it in 2009 from omni- (all) and shambles (a mess), and then newspapers stole it because it was funny and sharp. Though actually, shambles by itself already means a mess, so omnishambles is the same idea with a louder hat. Americans rarely say it; they would say a complete disaster or a total mess. It is not a kind word, but it is not a swear word either. You will meet it in British papers and political chat, not in science class, even though it sits next to omnipotent in the dictionary. You would not put it in a very formal exam essay unless you know the reader likes living, jokey English.