Neglect ache crossing South America (6)
I believe the answer is:
disuse
'neglect' is the definition.
(I've seen this before)
'ache crossing south america' is the wordplay.
'ache' becomes 'die' (dying is a kind of aching).
'crossing' is an insertion indicator.
'south' becomes 's' ('S' can be a synonym of 'south').
'america' becomes 'us' (abbreviation for the United States).
's'+'us'='sus'
'die' going around 'sus' is 'DISUSE'.
(Other definitions for disuse that I've seen before include "Fall into this state to be unemplyed? (6)." , "Neglect; desuetude" , "Issued (anag)" , "Neglect; abandonment" , "State of not being employed" .)