1. adjective
a) Being only one of a larger population.
A singular experiment cannot be regarded as scientific proof of the existence of a phenomenon.
b) Being the only one of the kind; unique.
Syn: individual, unique, exceptional, extraordinary, remarkable, curious, eccentric, funny, odd, peculiar, strange, rum, rummy, unusual, non-invertible
2. noun
A form of a word that refers to only one person or thing.
Wikipedia foundation.