A person (5)
(Other definitions for one that I've seen before include "doesn't count for much" , "Figure" , "Unity" , "Sole; identical" , "Identical; number" .)
'a person' is the definition.
(I know that person can be written as human)
This is the entire clue.
(Other definitions for human that I've seen before include "Characteristic of people" , "Like people" , "likely to err?" , "Mortal; compassionate" , "Fallible - person" .)