一只耳朵用英语怎么说

"An ear" is how you would refer to one ear in English. The phrase has its roots in the Old English word "eare", which was used to describe the organ of hearing.
Example sentences:
He has a small cut on his ear.
She pierced her ear when she was a teenager.
The doctor checked his patient's ear for any signs of infection.
Translations:
他的耳朵有一个小伤口。
她十几岁时穿了耳朵。
医生检查了病人的耳朵是否有感染的迹象。