Nervous, twice circling edge of dangerous whirlpool (9)
I believe the answer is:
charybdis
'whirlpool' is the definition.
(I know that Charybdis is a type of whirlpool)
'nervous twice circling edge of dangerous' is the wordplay.
'nervous' becomes 'chary' (chary means nervous or cautious).
'twice circling' becomes 'bdi' (I am not sure about this - if you are sure you should believe this answer much more).
'edge of' suggests the final letters (one of the letters on the edge of the word).
The last letter of 'dangerous' is 's'.
'chary'+'bdi'+'s'='CHARYBDIS'
Can you help me to learn more?
(Other definitions for charybdis that I've seen before include "Mythical whirlpool" , "Scylla's counterpart" , "Whirlpool, across from 14" , "Whirlpool opposite Scylla" , "monster" .)