A chamber fellow; a Spanish military term. Soldiers were in that country divided into chambers, five men making a chamber, whence it was generally used to signify companion.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
cambridge oak * camesaNathan Bailey's 1721 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes