E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
From the Latin lira (the ridge left by the plough), hence the verb de-lirare, to make an irregular ridge or balk in ploughing. Delirus is one whose mind is not properly tilled or cultivated, a person of irregular intellect; and delirium is the state of a person whose mental faculties are like a field full of balks or irregularities. (See PREVARICATION.)