SUBSTRAC'TION, noun In law, the withdrawing or withholding of some right. Thus the substraction of conjugal rights, is when either the husband or wife withdraws from the other and lives separate. The substraction of a legacy, is the withholding or detaining of it from the legatee by the executor. In like manner, the withholding of any service, rent, duty or custom, is a substraction for which the law gives a remedy.