The most common and most likely answer to this crossword clue is the 7 letter word WAYWARD
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More clues leading to the result WAYWARD
Buddy explains!

The straight part
We know that "Erratic" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case erratic = wayward.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 WAYWARD mean?
WAYWARD adjective- Given to wilful, perverse deviation from the expected norm; tending to stray
- Obstinate, contrary and unpredictable
- Not on target