The most common and most likely answer to this crossword clue is the 8 letter word FEIGNING
I've seen this crossword clue in The Times
F
E
I
G
N
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Buddy explains!
The straight part
We know that "Pretender’s action" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pretender’s action = feigning.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 FEIGNING mean?
FEIGNING verb- To make a false show or pretence of; to counterfeit or simulate.
- To imagine; to invent; to pretend.
- To make an action as if doing one thing, but actually doing another, for example to trick an opponent.
- To hide or conceal.
- Act of one who feigns; fakery; deceit.