Apter

Thou tremblest; and the whiteness in thy cheek Is apter than thy tongue to tell thy errand.

[I]t hath been many an honest man's hap to pass for the father of children he never begot; and if your worship should provide for the child, it may make the people the apter to believe […]

Would you deign to be my instructress, I should prove an apter scholar than if taught by Signor Rappaccini himself.