noun

• (obsolete) The act of creeping upon with secrecy or by surprise.
  "[…]the irregularities of the first motions, violent assaults, and importunities of temptations, sudden incursions, and obreptions, sins of mere ignorance and inadvertency […]"
• (Scots law, obsolete) Act of obtaining gifts of escheat by fraud or surprise.
  "In Mr John Maitland's action against Cardross, (vide 17th instant,) the Lords repelled Cardross's allegeances founded upon the impetrating of the gift of eschat from his Majesty by obreption expresso mendacio, or subreption celata veritate; because it appeared that there was a competition made by Cardross before the gift was past in Exchequer, and this same objection was made against it, that it was impetrated viis et modis;"
• (Catholic law) The inclusion of false statements in a petition for a rescript.
  "A dispensation from a minor impediment is not vitiated by obreption or subreption, even though the final cause alleged be false."