E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Ell (Anglo-Saxon eln, an ell).
It is said that the English ell was the length of Henry I.s arm, but the ordinary length of a mans arm is about a yard.
Give him an inch, and hell take an ell. Give him a little licence, and he will take great liberties, or make great encroachments. The ell was no definite length. The English ell was 45 inches, the Scotch ell only 37 inches, while the Flemish ell was three-quarters of a yard and a French ell a yard and a half. This indefinite measure expresses the uncertainty of the length to which persons will go to whom you give the inch of liberty. Some will go the French ell; whie others of more modesty or more limited desires will be satisfied with the shorter measures.