ell (n.1) Look up ell at Dictionary.com
unit of measure, Old English eln, originally "forearm, length of the arm" (as a measure, anywhere from a foot and a half to two feet), from PIE *el- (1) "elbow, forearm" (cognates: Greek olene "elbow," Latin ulna, Armenian uln "shoulder," Sanskrit anih "part of the leg above the knee," Lithuanian alkune "elbow").

The exact distance varied, in part depending on whose arm was used as the base and whether it was measured from the shoulder to the fingertip or the wrist: the Scottish ell was 37.2 inches, the Flemish 27 inches. Latin ulna also was a unit of linear measure, and compare cubit. The modern English unit of 45 inches seems to have been set in Tudor times.
Whereas shee tooke an inche of liberty before, tooke an ell afterwardes [Humfrey Gifford, "A Posie of Gilloflowers," 1580].
ell (n.2) Look up ell at Dictionary.com
name of the letter -L- in Latin; in reference to a type of building, 1773, American English; so called for resemblance to the shape of the alphabet letter.