The term 'fail completely' can be represented by four different crossword solutions: TANK (4 letters), Fallflat (8 letters), Comeacropper (12 letters) and Takeitonthechin (15 letters). TANK is a military term for an armored vehicle, and it can also be used to describe someone who is tough and resilient. Fallflat is an expression that means to fail or collapse suddenly and completely. Comeacropper is a British phrase that means to suffer a complete failure or defeat. Finally, Takeitonthechin is an idiom that means to accept a difficult situation without complaining. All of these terms can be used to describe the concept of failing completely.