No oxford english dictionary but here are the following:
The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
NOUN: 1. abbr. LCpl A noncommissioned rank in the U.S. Marine Corps that is above private first class and below corporal. 2. One who holds this rank.
ETYMOLOGY: From lancepesade, from obsolete French lancepessade, from Italian lancia spezzata, superior soldier : lancia, lance (from Latin lancea; see lance) + spezzata, feminine past participle of spezzare, to break to pieces ( Latin dis-, apart; see dis– + pezza, piece, from Medieval Latin pecia, piece, from Vulgar Latin *pettia).
\Lance`pe*sade"\, n. [F. lancepessade, lanspessade, anspessade, It. lancia spezzata a broken lance or demilance, a demilance roan, a light horseman, bodyguard.] An assistant to a corporal; a private performing the duties of a corporal; -- called also lance corporal.
Source: Webster's Revised Unabridged Dictionary, © 1996, 1998 MICRA, Inc.
And finally a link to website by a former marine sergeant who explains it pretty well.
To Join the Company of Military Historians click here