Perjury – Its Etymology
From the Tuesday April 9 entry from the Visual Thesaurus – Word of the Day
"Well I Swear! Word of the Day: perjury
The -jury part of today’s word is from the same source as the word jury but it’s pretty hard to get at the meaning by composition. Jury is ultimately from a Latin verb that means "swear," and the per- bit, in this case, means "beyond the limits." So perjury is beyond the limits of swearing, when the swearing is the kind where you’re supposed to be telling the truth under oath."