Indifference always blocks the way (6)
I believe the answer is:
apathy
'indifference' is the definition.
(synonyms)
'always blocks the way' is the wordplay.
'always' becomes 'ay'.
'blocks' is an insertion indicator (inserted letters are blocked in).
'the way' becomes 'path' ('path' can be a synonym of 'way').
'ay' going around 'path' is 'APATHY'.
(Other definitions for apathy that I've seen before include "Lack of interest or concern" , "Absence of interest or emotion" , "State of listlessness or disinterest" , "Disinclination to shift" , "Complete lack of interest, indifference" .)