Second hazard close to Scylla (4)
I believe the answer is:
beta
'second' is the definition.
(second Greek letter)
'hazard close to scylla' is the wordplay.
'hazard' becomes 'bet' (both can mean to gamble or risk).
'close to' indicates one should take the final letters (the 'close' to the word).
The final letter of 'scylla' is 'a'.
'bet'+'a'='BETA'
(Other definitions for beta that I've seen before include "It's next after alpha" , "less than perfect mark" , "software under test" , "character in Marathon" , "second class grade?" .)