Greek character very quietly swallowed by giant snake (5)
I believe the answer is:
kappa
'greek character' is the definition.
(letter of the Greek alphabet)
'quietly swallowed by giant snake' is the wordplay.
'quietly' becomes 'pp' (musical abbreviation for pianissimo).
'swallowed by' indicates putting letters inside.
'giant snake' becomes 'kaa' (I am not sure about this - if you are sure you should believe this answer much more).
'pp' going into 'kaa' is 'KAPPA'.
'very' acts as a link.
Can you help me to learn more?
(Other definitions for kappa that I've seen before include "Tenth Greek letter" , "letter from abroad" , "10th Greek letter" , "Greek K" , "Letter before lambda" .)