I might be hearing “icicle”, apparently (12)
I believe the answer is:
eavesdropper
'i' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for eavesdropper that I've seen before include "He may hear private confessions" , "Reproved apes (anag.)" , "One listens secretly" , "Secret listener" .)