Minor initially lacking in vision (6)
I believe the answer is:
slight
'minor' is the definition.
(thesaurus)
'initially lacking in vision' is the wordplay.
'initially' suggests taking the first letters.
'in' is an insertion indicator.
'vision' becomes 'sight' ('sight' can be a synonym of 'vision').
The initial letter of 'lacking' is 'l'.
'l' put inside 'sight' is 'SLIGHT'.
(Other definitions for slight that I've seen before include "Deliberately discourteous act" , "Not strongly built" , "Fragile - thin" , "Insubstantial; discourtesy" , "Insult, affront" .)