a. 1. Not settled in opinion; undetermined; wavering; hesitating in belief; also used, metaphorically, of the body when its action is affected by such a state of mind; as, we are doubtful of a fact, or of the propriety of a measure. [ 1913 Webster ]

Methinks I should know you, and know this man;
Yet I am doubtful. Shak. [ 1913 Webster ]

With doubtful feet and wavering resolution. Milton. [ 1913 Webster ]

2. Admitting of doubt; not obvious, clear, or certain; questionable; not decided; not easy to be defined, classed, or named; as, a doubtful case, hue, claim, title, species, and the like. [ 1913 Webster ]

Beauty is but a vain and doubtful good. Shak. [ 1913 Webster ]

Is it a great cruelty to expel from our abode the enemy of our peace, or even the doubtful friend [ i. e., one as to whose sincerity there may be doubts ]? Bancroft. [ 1913 Webster ]

3. Characterized by ambiguity; dubious; as, a doubtful expression; a doubtful phrase. [ 1913 Webster ]

4. Of uncertain issue or event. [ 1913 Webster ]

We . . . have sustained one day in doubtful fight. Milton. [ 1913 Webster ]

The strife between the two principles had been long, fierce, and doubtful. Macaulay. [ 1913 Webster ]

5. Fearful; apprehensive; suspicious. [ Obs. ] [ 1913 Webster ]

I am doubtful that you have been conjunct
And bosomed with her. Shak.

Syn. -- Wavering; vacillating; hesitating; undetermined; distrustful; dubious; uncertain; equivocal; ambiguous; problematical; questionable. [ 1913 Webster ]

adv. In a doubtful manner. [ 1913 Webster ]

Nor did the goddess doubtfully declare. Dryden. [ 1913 Webster ]

n. 1. State of being doubtful. [ 1913 Webster ]

2. Uncertainty of meaning; ambiguity; indefiniteness. “ The doubtfulness of his expressions.” Locke. [ 1913 Webster ]

3. Uncertainty of event or issue. Bacon. [ 1913 Webster ]