the GNU version of the Collaborative International Dictionary of English
adj. Not plausible; not wearing the appearance of truth or credibility, and not likely to be believed.
The Century Dictionary and Cyclopedia
Not plausible; not having the appearance of truth or credibility; of dubious aspect.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
adj. having a quality that provokes disbelief
adj. highly imaginative but unlikely
Word Usage
"But Bridge undercuts his credibility by describing early childhood and later events in implausible and gratuitous detail, including pages of line-by-line dialogue."