Doctor
noun, の adjective
A medicine expert is someone who knows a lot about medicine. Those people are (I hope) generally doctors.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
ついにあの医師の尻尾をつかまえたぞ！
We've finally got some proof to expose that doctor!
あっ、その医師って、テレビによく出てる方ですよね？
Oh, that doctor is on TV a lot, right?
ほんの短い時間だけでしたが、この医師は二度テレビに出たことがあるんです。
This doctor appeared on TV twice, though just for short amounts of time.
医師によると、祖父の心拍はだんだん弱くなっていって、最後に停止したそうです。
According to the doctor, my grandfather's heartbeat became gradually weaker and weaker, then it finally stopped.