- so extraordinary as to seem impossible: incredible speed.
- not credible; hard to believe; unbelievable: The plot of the book is incredible.
- beyond belief or understanding; unbelievable
- informal marvellous; amazing
early 15c., “unbelievable,” from Latin incredibilis “not to be believed,” from in- “not” (see in- (1)) + credibilis “worthy of belief” (see credit). Used c.1400 in a now-extinct sense of “unbelieving, incredulous.” Related: Incredibly.