The most common and most likely answer to this crossword clue is the 6 letter word DAIMON
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More clues leading to the result DAIMON
Buddy explains!

The straight part
We know that "a good spirit" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a good spirit = daimon.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DAIMON mean?
DAIMON noun- An evil supernatural spirit.
- A neutral supernatural spirit.
- Someone with great strength, passion or skill for a particular activity, pursuit etc.; an enthusiast.
- A form of patience (known as Canfield in the US).
- Any of various hesperiid butterflies of the genera Notocrypta and Udaspes.