Characterized by doubt; doubtful or uncertain (archaic or dialectal).
Formed from 'doubt' plus '-some,' an Old English suffix (from 'sum,' meaning 'some') that creates adjectives suggesting a quality or tendency. This appears in words like 'lonesome,' 'fearsome,' and 'awesome,' though 'doubtsome' is now archaic.
The '-some' suffix is actually older than '-ful' for expressing qualities, which is why we have 'awesome' but not 'awefull'—yet for doubt, English speakers preferred 'doubtful' to 'doubtsome,' probably because it sounded better and connected to Latin 'dubius.'
Complete word intelligence in one call. Free tier — 50 lookups/day.