The Collaborative International Dictionary of English v.0.48:

L \L\ ([e^]l), n.
   1. An extension at right angles to the length of a main
      building, giving to the ground plan a form resembling the
      letter L; sometimes less properly applied to a narrower,
      or lower, extension in the direction of the length of the
      main building; a wing. [Written also ell.]
      [1913 Webster]

   2. (Mech.) A short right-angled pipe fitting, used in
      connecting two pipes at right angles. [Written also
      ell.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ell \Ell\, n. [AS. eln; akin to D. el, elle, G. elle, OHG.
   elina, Icel. alin, Dan. alen, Sw. aln, Goth. alenia, L. ulna
   elbow, ell, Gr. ? elbow. Cf. Elbow, Alnage.]
   A measure for cloth; -- now rarely used. It is of different
   lengths in different countries; the English ell being 45
   inches, the Dutch or Flemish ell 27, the Scotch about 37.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ell \Ell\, n. (Arch.)
   See L.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ell
    n 1: an extension at the end and at right angles to the main
         building