Obscurity leads to half the errors (4)
I believe the answer is:
mist
'obscurity' is the definition.
(thesaurus)
'half the errors' is the wordplay.
'half' indicates taking half.
'the errors' becomes 'mistakes' ('mistake' can be a synonym of 'error').
'mistakes' cut in half is 'MIST'.
'leads to' is the link.
(Other definitions for mist that I've seen before include "Cloud; thin fog" , "Slight fog" , "Haze" , "Watery vapour" , "Watery film" .)