Speak evil of a worker wanting to do harm (9)

I believe the answer is:

malignant

I'm a little stuck... Click here to teach me more about this clue!

'wanting to do harm' is the definition.
I can't tell whether this defines the answer.

'speak evil of a worker' is the wordplay.
'speak evil of' becomes 'malign' (I've seen this before).
'a worker' becomes 'ant' (worker is a type of ant).
'malign'+'ant'='MALIGNANT'

Can you help me to learn more?

(Other definitions for malignant that I've seen before include "Bent on harming" , "Evil, malevolent" , "Feeling or showing great ill will, cancerous" , "Spiteful" , "Very bad" .)

I've seen this clue in The Globe and Mail.

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