The term 'LONGEST SENTENCE' can be solved by the four letter word 'LIFE'. LIFE is a concept that has been studied and discussed for centuries. It is often used to refer to the experience of being alive, but it can also refer to the physical existence of living organisms. The longest sentence ever written is believed to be a sentence in the novel 'Gadsby' by Ernest Vincent Wright, which is composed of over 180, 000 words and is said to be around 3, 300 words long.