Why was Yonah displeased?
Rashi: He said, now the Nochrim will think that I am a false Navi. Radak - Hashem told him via Ru'ach Nevu'ah that He retracted from His decree, since they repented.
Radak: This was bad for Yisrael - [the Nochrim repented, but] Yisrael did not repent from their evil way.
Malbim citing Mahari: This 'Ra' was illness due to depression; he wanted to die. He thought that the decree will be canceled only if they repent also in Emunos and mindsets (belief in idolatry); they repented only in deeds. He understood that Hashem left them to be a staff of anger against Yisrael. It pained him that he was the cause to sustain this staff. He wanted to die rather than do so! Also, it pained him that idolaters will overpower Yisrael.
What is the root of "va'Yera"?
Radak: It is Yera. The same applies to "va'Yera b'Einei Hashem" (Bereishis 38:10), "Tera Eino" (Devarim 28:44) and all similar words. This is unlike [the grammarian] R. Yehudah 1 .
R. Yehudah holds that it is a two letter root (Reish Ayin), or there is a Vov or Yud in the middle. (PF)