I read somewhere, enthusiasm come from a word, to be filled by God, so in a Crhistian parlance, for example, it means to be filled with The holy spirit. So to remain enthusiastic, be led by the Holy...
The English term 'enthusiastic' means having or showing great excitement and interest
You spelled it correctly.
What is the opposite of enthusiastic ?Spiritless
Keen, eager, willing, zealous and excited