Perhaps overdone out of slavishness? (6)

I believe the answer is:

lavish

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'perhaps overdone out' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?

'of slavishness?' is the wordplay.
'of' says the answer is hidden in the clue.
'LAVISH' is hidden in the letters of 'slavishness'.

Can you help me to learn more?

(Other definitions for lavish that I've seen before include "shower" , "Generous - liberal" , "Lash around Vi is extravagant (6)" , "Luxurious" , "Squander" .)

I've seen this clue in the Evening Standard.

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