Definition of "treasonable"

"I can feel," said he, "for a gentleman in your circumstances; but it is my duty to see that no communication takes place between yourself and the ladies involved in the suspicion of treasonable practices. Your farewells must be made in my presence."

1837, L[etitia] E[lizabeth] L[andon], Ethel Churchill: Or, The Two Brides. […], volume II, London: Henry Colburn, […], pages 121–122