Italian author incorporating Homer's principal nymph (4)
I believe the answer is:
echo
'nymph' is the definition.
(figure of Greek myth)
'italian author incorporating homer's principal' is the wordplay.
'italian author' becomes 'eco' (Umberto Eco).
'incorporating' means one lot of letters goes inside another.
'principal' indicates taking the first letters (principal letter).
The first letter of 'homers' is 'h'.
'eco' enclosing 'h' is 'ECHO'.
(Other definitions for echo that I've seen before include "copy" , "One who slavishly copies" , "Reminder" , "Noise heard again" , "A natural sound reflection" .)