Do not seek this word — meaning robbery or brigandage — in your dictionary, unless it be of the size and comprehensiveness of the Oxford English Dictionary: it is quite obsolete and vanished from the treasury of writers’ vocabularies more than a century ago. Indeed, the OED doesn’t have an example after 1732. In 1865, John Mitchell Bonnell listed latrociny in his Manual of the Art of Prose Composition as one of the many words “rejected by good writers, though properly formed”.
Clearly, nobody had told the anonymous reviewer of J J Audubon’s The Birds of America, which appeared in The American Whig Review of March 1845 (over 13 pages of small type: these were more leisurely days). He is being rude about John Gould, whose Birds of Europe had appeared some years before:
By a sagacious duplication so as barely to avoid the penalties consequent upon a direct infringment of copyright, he has managed to give his last four volumes a partially spirited tone, altogether foreign to the first. There are yet one or two instances of this cunning latrociny which occur to us as too rich not to be noted.
The original sense was of highway robbery and came from the Latin latrocinium for that activity, or for the band of robbers or brigands who practised it. To latrocinate, therefore, is to rob upon the highway. The same Latin root occurs in the even more obscure adjective latruncular, which refers to the ancient Roman game of latrunculi, robbers, which was something like chess or draughts (US checkers).