The Collaborative International Dictionary of English v.0.48:
Substraction \Sub*strac"tion\, n. [OF. substraction, F. soustraction. See Subtract.] 1. Subtraction; deduction. [Obs.] [1913 Webster] 2. (Law) See Subtraction, 3. [1913 Webster]Bouvier's Law Dictionary, Revised 6th Ed (1856):
SUBSTRACTION, French law. The act of taking something fraudulently; it is generally applied to the taking of the goods of the estate of a deceased person fraudulently. Vide Expilation.