Dangerous obstacle has the Italian horse retiring (6)
I believe the answer is:
lethal
'dangerous' is the definition.
Both the definition and answer are adjectives. Perhaps they are linked in a way I don't understand?
'obstacle has the italian horse retiring' is the wordplay.
'obstacle' becomes 'let' ('let' could historically mean an obstruction).
'has' is a charade indicator (letters next to each other).
'the italian' becomes 'la' ('the' in Italian).
'horse' becomes 'H' (synonyms).
'retiring' says the letters should be written in reverse.
'la'+'h'='lah'
'lah' reversed gives 'hal'.
'let'+'hal'='LETHAL'
Can you help me to learn more?
(Other definitions for lethal that I've seen before include "Murderous" , "All the change can be deadly." , "describing a killer?" , "Capable of causing death" , "Enough to cause death" .)