The most common and most likely answer to this crossword clue is the 8 plus 8 letter word TYMPANIC MEMBRANE
I've seen this crossword clue in The Times
T
Y
M
P
A
N
I
C
M
E
M
B
R
A
N
E
Buddy explains!
The straight part
We know that "eardrum" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case eardrum = tympanic membrane.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.