Molto is always only the first part of an instruction in music, because it means "much" or "very." Very what? Much what? That’s in the other part of the instruction!
For example, molto più animato means "much more lively," and molto espressivo means "very expressively" or "with much feeling." If adagio means "slow," what do you think molto adagio means? Molto is an Italian word and comes from Latin multum, which means "much" or "many." It’s related to the English form multi- as in multicultural, "including or involving many cultures." You can notice the same root in multiple and multiply as well.