Doctor
noun, の adjective
A medicine expert is someone who knows a lot about medicine. Those people are (I hope) generally doctors.
いし
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.
ほんの短い時間だけでしたが、あの医師は二度テレビに出たことがあります。
That doctor appeared on TV twice, though just for short amounts of time.