Eardrum
noun, の adjective
You can hear something beat because of a membrane in your ear called an eardrum. Make sure you don't stick your fingers too far in your ear or you could really hurt it.
こまく
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
そんなに大声を出されたら鼓膜が破れるよ。
If you play things that loudly you’ll tear your eardrums.