adj.
1 feeling doubt
VERBS
▪ be , feel , look , seem , sound
▪
Eric was far from sure and Marion looked ~.
▪ become
▪ remain
ADVERB
▪ extremely , fairly , very , etc.
▪ a little , slightly , etc.
PREPOSITION
▪ about
▪
She was rather ~ about the wisdom of eating the seafood.
2 unlikely
VERBS
▪ be , look , seem
▪ remain
ADVERB
▪ extremely , fairly , very , etc.
▪ highly
▪
Even if we could go, which is highly ~, John wouldn't be able to come with us.
▪ increasingly
▪ a little , slightly , etc.
Doubtful is used with these nouns: ↑ expression , ↑ legality , ↑ look , ↑ origin , ↑ validity , ↑ value