Crossword Genius

What I do with husband's third child (4)

Ross

I believe the answer is:

seth

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

'third child' is the definition.
(I've seen this before)

'what i do with husband's' is the wordplay.
I cannot really see how this works, but
'do' could be 'set' (synonyms) and 'set' is present in the answer.
'husband' could be 'h' and 'h' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for seth that I've seen before include "One of the first men" , "Vikram --, Indian author" , "Cain and Abel's younger brother" , "Indian writer" , "Younger brother to Cain and Abel" .)

I've seen this clue in The Times.
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