Dad sets off, most depressed (7)

I believe the answer is:

saddest

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'most depressed' is the definition.
Both the answer and definition are superlative adjectives. Maybe you can see a link between them that I can't see?

'dad sets off' is the wordplay.
'off' indicates anagramming the letters.
'dad'+'sets'='dadsets'
'dadsets' is an anagram of 'SADDEST'.

Can you help me to learn more?

(Other definitions for saddest that I've seen before include "Most doleful" , "Most unhappy" , "most dejected" , "Most gloomy" , "Most blue" .)

I've seen this clue in The Daily Express.

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