plagiarius

from Bouvier's Law Dictionary, Revised 6th Ed (1856)
PLAGIARIUS, civil law. He who fraudulently concealed a freeman or slave who 
belonged to another. 
     2. The offence itself was called plagium. 
     3. It differed from larceny or theft in this, that larceny always 
implies that the guilty party intended to make a profit, whereas the 
plagiarius did not intend to make any profit. Dig. 48, 15, 6; Code, 9,  20, 
9 and 15. 
    

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