Ell
Old English eln, of Germanic origin; from an Indo-European root shared by Latin ulna (see ulna). Compare with elbow and also with cubit (the measure was originally linked to the length of the human arm or forearm).
wiktionary
From Middle English elle, elne, from Old English eln(“the length of the forearm from the elbow to the tip of the middle finger; a unit of measure”), from Proto-Germanic *alinō, from Proto-Indo-European*Heh₃l-én-eh₂, from *Heh₃l-(“elbow, forearm”). Cognate with Dutch el(“ell”), German Low German Ell(“ell”), German Elle(“ell”), Swedish aln(“cubit; ell”), Icelandic alin(“cubit; ell”), Latin ulna(“forearm”).
From the name of the letter L
etymonline
ell (n.1)
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 root *el- "elbow, forearm." 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)
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.
