Fact (5)
'fact' is the definition.
(singular form of 'data')
This is the entire clue.
(Other definitions for datum that I've seen before include "Basic fact" , "Unit of dope" , "Fixed starting point for measurements" , "Single informative fact" , "Fact or stat" .)
'fact' is the definition.
(I know that truth is a type of fact)
This is all the clue.
(Other definitions for truth that I've seen before include "Veracity; established fact" , "known facts" , "Gospel" , "Candour" , "real story" .)
'fact' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for reality that I've seen before include "The way things actually are" , "Verisimilitude" , "Actual existence" , "Truth, actuality" , "The way things are, no illusions" .)