The most common and most likely answer to this crossword clue is the 8 letter word UPSTAGED
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Buddy explains!

The straight part
We know that "Overshadowed" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case overshadowed = upstaged.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 UPSTAGED mean?
UPSTAGED verb- To draw attention away from others, especially on-stage.
- To force other actors to face away from the audience by staying upstage.
- To treat snobbishly.
- To restage (cancer) to a higher stage than that found at last assessment (compare downstage).