South American iron is reliable (4)
I believe the answer is:
safe
'reliable' is the definition.
(I've seen this in another clue)
'south american iron' is the wordplay.
'south american' becomes 'SA'.
'iron' becomes 'Fe' (Fe is the chemical symbol for iron).
'sa'+'fe'='SAFE'
'is' is the link.
(Other definitions for safe that I've seen before include "Free from risk" , "Protected from danger" , "Iron box in which to keep money or important papers" , "Harmless" , "Unharmed" .)