A doubtful person or thing.
"The jury returned a verdict that left many observers feeling doubtful about whether justice was truly served."
open to doubt or suspicion
"the candidate's doubtful past"
"he has a dubious record indeed"
"what one found uncertain the other found dubious or downright false"
"it was more than dubitable whether the friend was as influential as she thought"
Subject to, or causing doubt.
"The future of the project remains doubtful given the sudden loss of funding."