Undiscovered (6)
(Other definitions for latent that I've seen before include "Potential, dormant" , "Potential not realised" , "Existing but hidden" , "waiting to be discovered" , "Existing but not yet manifest" .)
'undiscovered' is the definition.
(similar in meaning)
This is all the clue.
(Other definitions for unknown that I've seen before include "Strange - obscure" , "Not familiar" , "Obscure, unheard-of, nameless" , "Anonymous" , "x, y or z, possibly" .)