adv. In a subtle manner; slyly; artfully; cunningly. [ 1913 Webster ]
Thou seest how subtly to detain thee I devise. Milton. [ 1913 Webster ]
In the nice bee what sense so subtly true. Pope. [ 1913 Webster ]
Subtly communicating itself to my sensibilities, but evading the analysis of my mind. Hawthorne. [ 1913 Webster ]