The Collaborative International Dictionary of English v.0.48:

Lintel \Lin"tel\ (l[i^]n"t[e^]l), n. [OF. lintel, F. linteau,
   LL. lintellus, for limitellus, a dim. fr. L. limes limit. See
   Limit.] (Arch.)
   A horizontal member spanning an opening, and carrying the
   superincumbent weight by means of its strength in resisting
   crosswise fracture.
   [1913 Webster] Lintie

WordNet (r) 3.0 (2006):

lintel
    n 1: horizontal beam used as a finishing piece over a door or
         window [syn: header, lintel]

The Jargon File (version 4.4.7, 29 Dec 2003):

Lintel
 n.

    The emerging Linux/Intel alliance. This term began to be used in early
    1999 after it became clear that the Wintel alliance was under increasing
    strain and Intel started taking stakes in Linux companies.