Partner, extremely chivalrous, rejected Greek nymph (6)
I believe the answer is:
scylla
'greek nymph' is the definition.
'scylla' can be an answer for 'nymph' (I've seen this before). I am not sure about the 'greek' bit.
'partner extremely chivalrous rejected' is the wordplay.
'partner' becomes 'ally' (I've seen this in other clues).
'extremely' says to hollow out the word (remove centre letters).
'rejected' says the letters should be written in reverse.
'chivalrous' with its middle taken out is 'cs'.
'ally'+'cs'='allycs'
'allycs' reversed gives 'SCYLLA'.
Can you help me to learn more?
(Other definitions for scylla that I've seen before include "Mythic sea nymph transformed into a sea monster who devoured sailors" , "Artificial cave" , "Mythical sea monster" , "In Greek myth, sea monster who lived in cave opposite whirlpool Charybdis" , "Rock, across from 21" .)