- In <em>mathematics</em>, unambiguous and singly determinate.
- Only; single.
- Having no like or equal; unmatched; sole; unequaled; single in its kind or excellence: often used relatively, and then signifying rare, unusual.
- A unique thing; a thing unparalleled or sole of its kind.
- A thing without a like; something unequaled or unparalleled.
- Being without a like or equal; unmatched; unequaled; unparalleled; single in kind or excellence; sole.
- Being the only one of its <xref>kind</xref>; <xref>unequaled</xref>, <xref>unparalleled</xref> or <xref>unmatched</xref>.
- Of a feature, such that only one holder has it.
- Of a <xref>rare</xref> <xref>quality</xref>.
- A thing without a like; something unequalled or unparallelled.
- the single one of its kind
- highly unusual or rare but not the single instance
- radically distinctive and without equal
- (followed by `to') applying exclusively to a given category or condition or locality