It's neglectful of a route by the end (6)
I believe the answer is:
apathy
'it's neglectful' is the definition.
I can't judge whether this defines the answer.
'a route by the end' is the wordplay.
'route' becomes 'path' (synonyms).
'the end' suggests the final letters.
The final letter of 'by' is 'y'.
'a'+'path'+'y'='APATHY'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for apathy that I've seen before include "Disinclination to shift" , "Complete lack of interest, indifference" , "Lack of emotion and interest" , "Absence of emotion or enthusiasm" , "Impassivity - lack of feeling" .)