I'm a L34 Summoner, so have leveled up Thaumaturge to L15, but his Thunder spell is not showing up as a cross class spell when playing arcanist/summoner. I did level up a conjuror to L8 for Protect and Aero, so is that the problem? I see utubes of arcanists casting "thunder" so what am I missing? I can use Aero instead, but Thunder is a bit more powerful.

Probably something simple.