Isha (医者) means "doctor." It refers to a medical professional who treats illness and injury. While "isha" is the noun for doctor, when addressing a doctor directly, it is polite to use "sensei" (先生) as an honorific, showing respect for their profession. Example: 彼は医者になりたいです。(Kare wa isha ni naritai desu.) = He wants to become a doctor.

病気(びょうき)や怪我(けが)を治療(ちりょう)する専門家(せんもんか)を指(さ)します。先生(せんせい)と呼(よ)ぶのが丁寧(ていねい)です。例(れい)：彼(かれ)は医者(いしゃ)になりたいです。