Slander sadist, slam for wickedness (13)

I believe the answer is:

dastardliness

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'wickedness' is the definition.
The answer and definition can be both human attributes as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

'slander sadist slam' is the wordplay.
'slam' is an anagram indicator (I've seen 'slammed' mean this).
'slander'+'sadist'='slandersadist'
'slandersadist' anagrammed gives 'DASTARDLINESS'.

'for' is the link.

Can you help me to learn more?

(Another definition for dastardliness that I've seen is " Wickedness, cruelness".)

I've seen this clue in The Hindu.

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