When faced with a difficult decision, it is better not to take unnecessary risks. Also when in doubt, abstain and when in doubt, leave it out

(uncommon) Capable of being doubted; doubtful; dubious; dubitable. See usage notes below. / (obsolete) Fearsome; redoubtable.

In a doubting manner.

plural of doubter

One who doubts.

In a doubtful manner, in context of doubt or ambiguity, questionably.

(sometimes proscribed) Without question; indubitably. / (obsolete) Without feeling doubt, without misgivings.

Without doubt; very probably, in all likelihood; doubtlessly.

Characterized by or experiencing no doubt at all, certain; undoubted; undoubting. / (obsolete) Free from fear or suspicion.

the property of being doubtless