Roget's 21st Century Thesaurus, Third Edition Copyright © 2013 by the Philip Lief Group.

WORD ORIGIN

late 14c., from doubt (n.) + -ful. Related: Doubtfully; doubtfulness.

MORE RELATED WORDS FOR UNDOUBTFUL

Roget's 21st Century Thesaurus, Third Edition Copyright © 2013 by the Philip Lief Group.