Supposititious

[...] the said pretended Testament was supposititious, & contriued by such as meant to defraud both the heires female of the said king Henrie the 8. as well as these of his eldest sister [...]

Source: wiktionary

But it may bee some will here obiect and say; that the Haire, and Loue-lockes which they weare, are supposititious, false, and counterfeit, and not their owne: therefore they violate no Law of God, nor Nature, since the long Haire they vse, is but borrowed, and aduenticious, their owne being short enough: perchance, but little or none at all.

Source: wiktionary

[T]he queen [Mary of Modena] was brought to bed of a ſon, who was baptiſed by the name of James. This would, if any thing could at that time, have ſerved to eſtabliſh him on the throne; but so great was the animoſity againſt him, that a ſtory was propagated that the child was ſuppoſititious, and brought to the queen's apartment in a warming-pan.

Source: wiktionary

These supposititious children of the semigods are called Umskiptingar; whence nurses and midwives were strictly enjoined to watch constantly, and to hold the infant firmly in their arms, till it had had the benefit of baptism, lest they should furnish any opportunity for such a change.

Source: wiktionary